JPH0333712A - Scanning optical system and optical scanner - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a scanning optical system and an optical scanning device.

[Prior Art] An optical scanning device that optically scans a surface to be scanned by deflecting a light beam with an optical deflection device is well known in connection with laser printers, digital copying devices, laser facsimiles, and the like.

One of the conditions for good optical scanning with a light beam is the stability of the diameter of an imaged spot formed by the light beam on a surface to be scanned.

That is, if the diameter of the imaged spot changes with the imaged position, that is, the image height, during optical scanning, the size of pixels will be non-uniform when information is written, making it impossible to form a good information image.

One of the causes of such fluctuations in the imaging spot diameter is
This is the field curvature of the optical system of the optical scanning device.

Optical scanning devices that use deflection devices such as rotating polygon mirrors have a problem with so-called surface tilt. A known method is to use an anamorphic optical system in which the deflection reflection surface of the deflection device and the surface to be scanned have an approximately conjugate relationship in terms of geometrical optics. Since the power in the direction corresponding to the sub-scanning direction becomes strong, when the curvature of field in the main scanning direction is corrected, strong curvature of field in the sub-scanning direction is likely to occur.

Furthermore, the applicant has previously proposed an optical scanning device with a simple structure that has a single lens with an approximate fθ function and a long toroidal lens (Japanese Patent Application No. 304737/1982).

In this optical scanning device, the long toroidal lens has the function of correcting field curvature in the main and sub-scanning directions, but it is difficult to use in terms of light utilization efficiency and mechanical arrangement of optical elements. Therefore, it is preferable to place the long toroidal lens as far away from the scanned surface as possible, but if you try to widen the field of view when you deploy the long toroidal lens as far away from the scanned surface as possible, This makes it difficult to correct field curvature in the sub-scanning direction.

As mentioned above, a method using a modified cylindrical lens having a convex saddle-shaped lens surface has been proposed as an effective method for correcting the curvature of field in the sub-scanning direction, which hinders uniformity of the imaging spot diameter. (Unexamined Japanese Patent Publication No. 61-120112
Publication No.).

[Problems to be Solved by the Invention] A modified cylindrical lens having a saddle-shaped lens surface is effective in correcting field curvature in the sub-scanning direction, but there is a problem in that it is not easy to manufacture.

In other words, a modified cylindrical lens with a saddle-shaped lens surface is long, so it is practical to mold it using synthetic resin, but due to the special nature of the saddle-shaped lens surface, it is difficult to mold the lens surface It is difficult to make a mold with a concave surface.

For example, one possible method for manufacturing a concave mold is to first make a corresponding mold with a convex surface, and then transfer this convex surface by electroforming to obtain a concave mold. Considering the decrease in accuracy, in order to obtain a highly accurate concave surface, extremely high precision is required for the convex surface to be transferred, and the precision of the concave surface that can be obtained by transfer is naturally limited. , it is extremely difficult to create a concave mold with the necessary precision.

The above-mentioned Japanese Unexamined Patent Publication No. 120112/1988 discloses a cutting method as a method for producing a saddle-shaped lens surface.

The cutting method is not suitable for mass production as a lens manufacturing method, so
It is difficult to reduce the cost of the scanning optical system and, by extension, the optical scanning device.

The present invention was made in view of the above-mentioned circumstances, and
The purpose is, firstly, to provide a novel scanning optical system that can satisfactorily correct the curvature of field in the sub-scanning direction and has good mass productivity (invention of claim 1), and secondly, it has a simple configuration. Moreover, the present invention aims to provide a novel optical scanning device which can be realized at low cost and which can realize good optical scanning (inventions according to claims 2 to 5).

[Means for Solving the Problems] The scanning optical system according to claim 1 which characterizes the present invention is as follows: “In an optical scanning device that optically scans a surface to be scanned by deflecting a light beam by an optical deflection device,
"Optical system installed between the above-mentioned optical deflection device and the surface to be scanned"
``The function of forming an image of the deflected light beam on the surface to be scanned, and also making the deflection origin of the light beam and the surface to be scanned in a substantially conjugate relationship in terms of geometric optics in the sub-scanning direction.''
has.

The optical scanning device according to claims 2 to 5 is characterized in that the concave lens surface includes a barrel-shaped toroidal surface whose radius of curvature in the sub-scanning direction becomes smaller as the distance from the optical axis increases in the main-scanning direction. This is an optical scanning device that uses a scanning optical system.

An optical scanning device according to a second aspect of the present invention includes a light source device, a collimating optical system, a cylindrical lens, a deflection device, an optical scanning lens, and a correction optical system.

The "light source device" emits a luminous flux.

The "collimating optical system" converts the light beam from the light source into a substantially parallel light beam6 The "cylindrical lens" forms the light beam that has been made into a substantially parallel light beam by the collimating optical system into a long linear image in the main scanning direction .

``The deflection device M has a deflection reflection surface near the imaging position of this line image, and deflects the light beam at a constant angular velocity.

The "light scanning lens" is composed of a plurality of lenses, and focuses the light beam deflected by the deflection device to scan the surface to be scanned at approximately constant speed.

The "correction optical system" is a long toroidal lens placed between the optical scanning lens and the scanned surface, and is a barrel whose radius of curvature in the sub-scanning direction becomes smaller as the optical axis moves away from the main scanning direction. 4. The light according to claim 3, which includes a toroidal surface as a concave lens surface, cooperates with an optical scanning lens to form a focused beam substantially on a surface to be scanned, and has a curvature of field in the main and sub-scanning directions. The scanning device includes a light source device, a focusing optical system, a cylindrical lens, a deflection device, a light scanning lens, and a correction optical system.

The "light source device" emits a luminous flux.

The "focusing optical system" converts the light beam from the light source device into a focused light beam.

The "cylindrical lens" focuses the light beam focused by the focusing optical system as a long line image in the direction corresponding to the main scanning in the vicinity of the deflection reflection surface of the deflection device.

The "deflection device" has a deflection reflection surface near the imaging position of this line image, and deflects the focused light beam by the focusing optical system at a constant angular velocity.

The "light scanning lens" is a single lens that further focuses the focused light beam deflected by the deflection device.

The surface to be scanned is scanned at approximately constant speed.

The "correction optical system" is a long toroidal lens placed between the optical scanning lens and the surface to be scanned, and is a barrel whose radius of curvature in the sub-scanning direction becomes smaller as the optical axis expands in the main-scanning direction. It includes a type toroidal surface as a concave lens surface, and works together with the optical scanning lens to substantially image the converging light beam onto the scanned surface, correcting the surface tilt of the deflection device, and forming an image plane in the main and sub-scanning directions. An optical scanning device according to a fourth aspect of the present invention characterized by curvature includes a light source device, a collimating optical system, a cylindrical lens, a deflection device, an optical scanning lens, and a correction optical system.

The "r light source device, collimating optical system, cylindrical lens, and deflection device" are the same as those in the optical scanning device of claim 2 above.

The "light scanning lens" is a single lens, and focuses the light beam deflected by the deflection device to scan the surface to be scanned at approximately constant speed.

The "correction optical system" is a long toroidal lens placed between the optical scanning lens and the scanned surface, and is a barrel whose radius of curvature in the sub-scanning direction becomes smaller as the optical axis moves away from the main scanning direction. 6. The light according to claim 5, which includes a toroidal surface as a concave lens surface, cooperates with an optical scanning lens to form a focused beam substantially on the surface to be scanned, and has a curvature of field in the main and sub-scanning directions. The scanning device includes a light source device, a focusing optical system, a cylindrical lens, a deflection device, a light scanning lens, and a correction optical system.

The "light source device, focusing optical system, cylindrical lens, and deflection device" are the same as those in the optical scanning device of claim 3 above.

The "light scanning lens" is composed of a plurality of lenses, and further focuses the light beam deflected by the deflection device in a direction corresponding to main scanning, thereby scanning the surface to be scanned at approximately constant speed.

"The correction optical system J is a long toroidal lens placed between the optical scanning lens and the surface to be scanned, and is a barrel whose radius of curvature in the sub-scanning direction becomes smaller as the optical axis moves away from the optical axis in the direction corresponding to the main scanning. It includes a toroidal surface as a concave lens surface, and works together with the optical scanning lens to substantially form an image of the focused light beam onto the surface to be scanned, thereby correcting the surface tilt of the deflection device, and also correcting the surface tilt in the main and sub-scanning directions. Correct field curvature.

Note that "main scanning direction" refers to the direction parallel to the main scanning direction when the optical path from the light source to the surface to be scanned along the optical axis is developed on the same plane, and in the above developed state. The direction parallel to the sub-scanning direction is the sub-scanning corresponding direction.

Regarding the barrel-shaped toroidal surface, the "radius of curvature in the sub-scanning direction" refers to both the optical axis of the lens system and the sub-scanning direction between the deflection reflection surface and the surface to be scanned in the above-mentioned developed state. The radius of curvature of the cut shape when a barrel-shaped toroidal surface is virtually cut with a plane parallel to .

In the optical scanning device according to claims 2 to 5, a long line image in a direction corresponding to the main scanning is formed in the vicinity of the deflection reflecting surface of the deflection device by the action of the cylindrical lens, but the main function of the cylindrical lens is to control the beam. The geometrical optical imaging position does not necessarily match the position of the reflected light reflecting surface.

[Function] The present invention and the inventions of claims 1 to 5 have in common that the lens system disposed between the deflection reflection surface of the deflection device and the scanned surface "has a barrel-shaped toroidal surface as a concave lens surface." It is a feature of

FIG. 5(I) shows a barrel-shaped toroidal surface.

Since this barrel-shaped toroidal surface is concave, it has negative power, but the radius of curvature in the sub-scanning direction directs the optical axis in the main-scanning direction (
In Fig. 5 (1), the negative power decreases as it moves away from the optical axis (in the left-right direction), so the negative power increases in the negative direction as it moves away from the optical axis in the main scanning direction, and the luminous flux incident on the barrel-shaped toroidal surface The tendency of focusing in the sub-scanning direction is weakened as the distance from the optical axis increases. This effect enables good correction of field curvature in the sub-scanning direction.

In other words, a long cylindrical lens has conventionally been used to correct field curvature, but the light beam incident on the long cylindrical lens is obliquely incident on the long cylindrical lens as the deflection angle increases. Since the power of the lens is apparently stronger than the normal power, strong hanging-type curvature of field with the concave surface facing the deflection device side is likely to occur in the sub-scanning direction.

However, the action of the barrel-shaped toroidal surface alleviates the convergence tendency of the incident light beam as the deflection angle increases, as described above, which effectively offsets the apparent increase in power and enables good field curvature correction. It is.

In the optical scanning device according to claims 2 to 5, since the optical system for correcting field curvature is a long toroidal lens and includes a barrel-shaped toroidal surface as a concave surface, better correction of field curvature is possible.

Further, since the barrel-shaped toroidal surface is a concave surface, when a lens including this surface is molded from resin, a mold with a convex surface may be used.

The barrel-shaped toroidal surface has a circular arc curve 10 as shown in FIG. If the distance from the rotation axis 2 to the circular arc curve 10 is r as shown in the figure with respect to the position MH in the direction of the rotation axis, and the maximum value of r is <ro as shown in the figure, then r is at position H of the barrel-shaped toroidal surface. Corresponding to the radius of curvature in the sub-scanning section, generally I r l = I r@ l - I Rl +f
It is expressed as (1). However, arc-shaped curve 1 with radius R
When the center of curvature of 0 is closer to the scanned surface than the barrel-shaped toroidal surface, r>O, ro>O, R>O1 When the center of curvature is closer to the deflection device than the barrel-shaped toroidal surface, r<0゜r, <0. The sign is set as R<0. At this time, Irl≦l
r.

It is 1.

Note that the shape of the above-mentioned arcuate curve 1io can be expressed by a well-known polynomial representing an aspherical surface, and its coefficients can be appropriately selected, and the barrel-shaped toroidal surface obtained from such a shape can be expressed as It is possible to perform field curvature correction with higher accuracy by using

Note that the focal length of the scanning optical system in the main scanning direction is fM
, when the distance from the lens surface on the scanning surface side of the correction optical system to the scanning surface is d = fl The scanning optical system used in the optical scanning device of equations 2, 3 and 4 is 0.8 > d /fyo＞
0.1 It is desirable to satisfy the condition (2).

Further, a scanning optical system of an optical scanning device according to claim 5 is provided.

0.6 > d/fa) 0.1
It is desirable to satisfy the following condition (3).

When the upper limits of these conditions (2) and (3) are exceeded, the curvature of field in the sub-scanning direction becomes excessive in an optical scanning device using a corresponding scanning optical system, and the variation in spot diameter due to image height becomes large.

If the lower limit is exceeded, in an optical scanning device using a corresponding scanning optical system, the apertures in the sub-scanning direction of the averte 7 that regulates the spot diameter of the light beam become smaller.

A problem arises in that the light transmission efficiency of the optical scanning device is reduced.

Therefore, it is desirable that conditions (2) and (3) above be satisfied.

All the embodiments related to each claim described below meet the above conditions (
2) and (3) are satisfied.

[Example J Hereinafter, a description will be given based on a specific example.

FIG. 1 shows an example of an optical scanning device implementing the invention of claim 2.

FIG. 1 shows the arrangement of the optical system in the optical scanning device developed along the optical path of the chief ray from the light source to the surface to be scanned.

FIGS. 1 (I-1) and (H-1) are views of the optical scanning device viewed from the sub-scanning direction, and in these figures, the vertical direction of the scanned surface 7 is the main scanning direction.

In addition, Fig. 1 ([-, 2) and (II-2) are views seen from the main scanning direction, and in this figure, the direction perpendicular to the drawing is the direction corresponding to the main scanning, and the vertical direction is the sub-scanning direction. This is the corresponding direction.

Now, in FIG. 1, the symbol 1 indicates a light source.As the light source 1, an LD or an LED is used. The light emitted from the light source 1 is converted into a substantially parallel light beam by the collimating lens 2 , the cross-sectional shape of the beam is shaped by the aperture 8 , and the beam is incident on the cylindrical lens 3 . As shown in the figure, the cylindrical lens 3 has power only in the sub-scanning direction, so the incident parallel light beam is near the deflection reflection surface 4 of the optical deflection device, with its longitudinal direction in the main-scanning direction. It forms an image as a line image. The cylindrical lens has a focusing effect in the direction corresponding to the sub-scanning, and also performs beam shaping in cooperation with the aperture, so the imaging position of the cylindrical lens is not necessarily set on the deflection and reflection surface.

The light deflection device is a rotating polygon mirror in this embodiment. The light beam is reflected by a polarizing reflective surface. This reflected beam is deflected as the deflection reflection surface rotates. Therefore, the deflection origin of the deflected light beam is the reflection position by the deflection reflection surface 4.

The optical system disposed between the deflection reflection surface 4 and the scanned surface 7 is the scanning optical system, and in this embodiment, the fθ lens 5 and the barrel-shaped toroidal lens e+A (6B) constitute the scanning optical system. There is.

The fθ lens 5 is arranged in the direction corresponding to main scanning, that is, in the direction corresponding to the main scanning direction.
I-1) and (II-t), the light beam is imaged on the surface to be scanned 7. That is, when viewed from the sub-scanning direction, the fθ lens 5 forms an image at infinity on the object side onto the scanned surface 7.

The focal length in this imaging is the focal length of the scanning optical system in the main scanning plane.

On the other hand, in the direction corresponding to the sub-scanning, the fθ lens 5 and the inserted toroidal lens 6A (6B) establish a substantially conjugate relationship between the deflection origin and the surface to be scanned 7. Therefore, (I-2
), (II-2), the image of the above-mentioned line image at the deflection starting point is the image of the fθ lens 5 and the inserted toroidal lens 6A (6
An image is formed on the scanned surface 7 by the action of B). Thus, the light beam forms a spot image on the surface to be scanned 7, and by deflecting the light beam with the optical deflector, the surface to be scanned 7 is scanned by the imaged spot. This scanning is the main scanning.

Next, the fθ lens 5 will be explained. The fθ lens 5 is
In this embodiment, there are two sheets, and the specifications are given as follows. That is, as shown in Figure 5, from the side of the deflection reflection surface 4 to the side of the scanned surface 7, the radius of curvature of the i-th lens surface is r, (i=1 to 4), and the distance between the i-th surfaces is d. ,
(i=1 to 3), and the refractive index of the j-th lens is n*(
j=L2), these have the following values.

i r, d negative jnjl
-186,012,711,511182-
103,03,4 3-440,018,621,768054-99,4
84 Note that the distance (referred to as do) from the deflection reflection surface 4 to the first lens surface of the fθ lens 5 is 26-0. The focal length of the fθ lens 5 is 120.0. Further, the fθ characteristic of this fθ lens 5 is ±0.5% or less.

Now, in the embodiment described with reference to FIG. 1, the features of the invention according to claim 1 are realized by the barrel-shaped toroidal lens 6. As shown in FIG.

This suspended toroidal lens 6A (6B) is a lens having a suspended toroidal surface as a concave lens surface.

For the barrel-shaped toroidal L/lens, the concave surface is directed toward the deflection/reflection surface 4 as shown in 6A, and the concave surface is directed toward the scanned surface 7 as shown in 6B.
It is possible to point it towards the side of

The lens surface on the opposite side of the insertion toroidal surface is a convex toroidal surface in this embodiment, but various other surface shapes are also acceptable.

Below, six specific examples of barrel-shaped toroidal lenses will be given.

In these six embodiments, L is the distance between the deflection reflection surface 4 and the scanned surface 7, and d4 is the distance between the fourth lens surface of the fθθ lens surface and the fθ lens side lens surface of the inserted toroidal lens. , d is the thickness of the inserted toroidal lens, d is the distance between the lens surface on the scanned surface side of the inserted toroidal lens and the scanned surface 7, and n' is the refractive index of the inserted toroidal lens.

Furthermore, between the barrel-shaped toroidal surface of the inserted toroidal lens and the toroidal surface paired therewith, the former, that is, the barrel-shaped toroidal surface, is expressed by the above equation (1), so it is defined by ro and R. . For the toroidal surfaces forming a pair of pJ-type toroidal surfaces, the radius of curvature in the main scanning direction is rk.
x, the radius of curvature in the sub-scanning direction is represented by ro, where the subscript k is 5 or 6, and when the toroidal surface is on the fθθ lens surface side, = 5, and when it is on the scanned surface 70R, JC = 6.

Examples 1 to 3 are examples in which a barrel-shaped toroidal surface is used on the surface to be scanned (aspects shown in FIG. 1 (I-1) and (I-2)), and Examples 4 to 6 are examples in which a barrel-shaped toroidal surface is used on the scanned surface side. The surface is fθθ
Examples using lens surfaces (Figure 1 (II-1), (II-
2).

Further, each of the examples has a deflection angle of 105.6 degrees and an effective writing width of 219.4 degrees, which is an ultra-wide angle.

Example 1 L (L di d@ r1
'182.5 58.8 3.0 60.0
1.48519rsx ray ro
R100010,8520,001000 Example 2 L d 4 d s d G
n '182.5 8g, 8 3.0 30
．． 0 1.48519r5X r sv
ro R15008,5020,001500 Example 3 L d 4 d s d 6n18
2.5 28.8 3.0 90.0 1.
48519rsx ray ro R
70011,6520,00700 Example 4 L d 4 d s d
s n '182.5 58.8
3.0 60. Oro Rrsx
r@y-20,00-850-850-10
, 5 Example 5 182.5 r.

-20,00 Example 6 Ld4dsd6 182.5 28.8 3.0 90.0rO
RrIlx rsy -20,00-700-700-11,50 As a comparative example, an example in which a long cylindrical lens is used instead of a suspended toroidal lens will be given.

The radius of curvature of the fOO lens surface of the long toroidal lens is rSXtr &
V, the radius of curvature of the lens surface on the side of the scanned surface is rsx and rsy in the main and sub-scanning directions, respectively, and the radius of curvature is 1.4851
9 1.48519 1.48519 6 30, O 5v -8,00 4 88,8 800 Refractive index 1 engineering n.

Comparative example 1 L d 4 d s d @
n182.5 5g, 8 3.0 60.0
1.485]9rsx rSv
rsx rsv200 21.0
200 ■Figure 6 shows the case of the above embodiment 3,
FIG. 2 is a diagram showing a specific configuration of an optical scanning device. The reference numeral 9 indicates a mirror, and the reference numeral 7^ indicates a photoreceptor forming a surface to be scanned, and the reference numeral 100 indicates a synchronization detection system for synchronizing optical scanning.

FIG. 7 shows the curvature of field in Example 2.

In this example, the distance between the inserted toroidal lens and the scanned surface is d@=60+em, and the field curvature is 4.
It is about 0, which is good.

In each curvature of field diagram, the solid line represents the curvature of field in the sagittal direction, that is, the sub-scanning direction, and the broken line represents the curvature of field in the meridional direction, that is, the main scanning direction.

FIG. 8 shows the field curvature related to Example 2.

This example is an example in which the barrel-shaped toroidal surface faces the surface to be scanned as in Example 1, but compared to Example 1, the inserted toroidal lens is placed closer to the surface to be scanned 7 (ds =
30 mm), and the field curvature is very well corrected.

FIG. 9 shows the field curvature for Example 3.

This example is also an example in which the insertion toroidal lens faces the scanned surface as in Example 1, but compared to Example 1, the insertion toroidal lens is placed farther away from the scanned surface 7 (d6=
901111), and the field curvature is slightly larger than in Examples 1 and 2.

FIG. 10 shows the curvature of field for Example 4.

In this example, d = 60 mm, and the mounting toroidal surface is directed toward the fθ lens side. Although the direction of the mounting toroidal surface is opposite to that of Examples 1 to 3 above, the field curvature is extremely small. In good condition.

FIG. 11 shows the field curvature for Example 5.

In this example, dll is 30 mm, and the toroidal surface of the frame is directed toward the fθ lens, but the curvature of field is extremely good.

FIG. 12 shows the field curvature for Example 6.

In this embodiment, d@=90 m<2> and the mounting toroidal surface is directed toward the f.theta. lens. Field curvature is Example 4
, 5, and the curvature of field is slightly improved compared to Example 3.

Comparing Figures 7 to 9 with Figures 10 to 12, it is clear that when using an inserted toroidal lens with the toroidal surface facing the fO lens side, it is better to use the inserted toroidal lens with the toroidal surface facing the scanned surface. It can be seen that this is slightly better than using the

No. 13 @ shows the curvature of field related to Comparative Example 1. In Comparative Example 1, the distance d between the long toroidal lens and the scanned surface is 80w+m, but the curvature of field is different from Examples 3 and 6. It is about the same level. From this, it can be seen that the suspended toroidal surface can be disposed at a considerable distance from the surface to be scanned and still have the effect of correcting field curvature. Therefore, a suspended toroidal lens is better than a long toroidal lens! 2. Great degree of freedom in installation location.

Since there can be a large distance between the inserted toroidal lens and the surface to be scanned, a barrel-shaped toroidal lens 6A can be placed between the mirror 9 and the fθ lens 5 as shown in FIG.

The invention of claim 3 will be described in detail below.

FIG. 2 shows the basic configuration of an optical scanning device according to a third aspect of the present invention, similar to FIG. 1.

Figures 2 (I-1) and (II-1) are views of the optical scanning device viewed from the sub-scanning direction, and Figures 1 (I-2) and (
II-2) is a diagram seen from the main scanning direction.

Now, in FIG. 2, reference numeral 11 indicates a light source. As the light source 11, an LD, an LED, or the like is used. Second
In the figure, an LD is assumed as the light source device 11. The light source 11 is arranged on the object-side optical axis of a condensing lens 12 as a condensing optical system, and makes a single divergent light beam enter the condensing lens 12 .

Now, the light beam incident on the condenser lens 12 is converted into a convergent light beam, and if there is nothing on the image side of the condenser lens 12, the image is formed at a natural convergence point, that is, point Q' on the image plane 17A.

In FIG. 2, reference numeral 18 indicates an aperture.

In FIG. 2, reference numeral 14 schematically depicts a deflection reflection surface of the deflection device. As the deflection device, a device that deflects the light beam at a constant angular velocity, such as a polygon mirror or a pyramidal mirror, is used.

The light beam focused by the focusing lens 12 is focused by the cylindrical lens 13 which has positive power only in the sub-scanning direction.
An image is formed in the vicinity of the deflection reflection surface 14 as a long line image in the direction corresponding to the main scanning. Since the cylindrical lens also has a beam shaping effect, the imaging position of the cylindrical lens is not necessarily set on the deflection/reflection surface, as in the apparatus of claim 1.

When the beam focused by the condensing lens 12 is deflected by the deflection device, the image forming point moves on the circular arc 19.

When the deflection device is a polygon mirror, the starting point of deflection varies slightly on the optical axis, so the locus of the imaging point does not become a perfect circular arc, but has a shape close to circular arc 19.

The deflected light flux first enters the optical scanning lens 15. This optical scanning lens 15 is a single lens having a positive refractive index, and is arranged between the deflection device and the scanned surface 17. Between the optical scanning lens 15 and the scanned surface 17, there is further a long toroidal lens 16A which is a correction optical system.
(1613) is deployed. This long toroidal lens 16A (16B) has strong positive refractive power in the sub-scanning direction.

The optical scanning lens 15 further focuses the incident focused light beam using its positive refractive power. The elongated toroidal lens 16A (16B) cooperates with the optical scanning lens 15 to form a beam of light into a spot-like image substantially on the surface to be scanned 17. Therefore, when the light beam is deflected at a constant angular velocity by the deflection device, the spot-shaped imaging point moves in the main scanning direction on the scanned surface 17 and optically scans the scanned surface. What are the optical scanning lens 15 and the long toroidal lens 16A (16B)?

The locus 19 of the natural focal point Q' is defined as an object plane, and an image of this object plane is formed on the scanned surface 17. In other words, the optical scanning lens 15 and the long toroidal lens 16A (16B) work together to link the locus 19 and the surface to be scanned 17 in a conjugate relationship with respect to the main scanning direction.

The main function of the long toroidal lens 18A (16B>) is to correct field curvature.In this field curvature correction function, the toroidal surface of the insert included in the long toroidal lens 16A (16B) as a concave surface is , plays an important role in correcting field curvature, especially in the sub-scanning direction.

The lens surface on the opposite side of the insertion toroidal surface is a convex toroidal surface in the embodiment described below, but various other surface shapes are also acceptable.

Hereinafter, 10 specific examples of the optical scanning device according to claim 3 will be given.

For these ten embodiments, a common optical scanning lens is used as the optical scanning lens 15.

The elements of this optical scanning lens are as follows.

As shown in FIG. 2, the radius of curvature of the first surface, that is, the lens surface on the deflection device side, is rl, the radius of curvature of the second surface, that is, the lens surface on the side to be scanned 16, is rl, the wall thickness is dl, and the refractive index is Assuming n, these are as follows.

rl rz dB n-
160-60, 219151, 57221 Also, the focal point ff of this optical scanning lens [1f=1so, the distance D from the deflection surface 13 to the natural focusing point Q'=548.1°, and the distance from the deflection surface 13 to the above-mentioned first surface The distance to fid0 is 28.0.

In addition, as shown in FIG. 2, L is the deflection surface 13 and the scanned surface 1.
Regarding the elongated toroidal lens of each example, d2 is the distance between the second lens surface of the light scanning lens 15 and the lens surface of the inserted toroidal lens 18 on the light scanning lens 15 side, and d3 is the distance between the inserted toroidal lens 15 and the long toroidal lens of each example. Thickness of the suspended toroidal lens 18, d
4 is the distance between the lens surface of the suspended toroidal lens 18 on the surface to be scanned 16 and the surface to be scanned 16, and n' is the distance.

The refractive index of the inserted toroidal lens 18 is shown.

Further, the toroidal surface of the toroidal lens is defined by <ro and R as described above. Regarding the toroidal surface, the radius of curvature in the main scanning direction is expressed as rbx, and the radius of curvature in the sub-scanning direction is expressed as rkV, where the subscript k is 3 or 4, and the toroidal surface is on the optical scanning lens 15 side. When it exists, =3, and when it exists on the scanned surface 17 side, =4.

Examples 7 to 15 are examples in which the inserted toroidal surface is used on the optical scanning lens side (cases in FIG. 2 (I-1) and (I-2)), and Example 16 uses the inserted toroidal surface on the optical scanning lens side. Example of use on the scanned surface side (Figure 2 (II-1), (II-2)
).

In addition, in each example, the deflection angle is 90 degrees, and the effective writing width is approximately 226 degrees.
Close and super wide angle.

Example 7 L d 2d s d 4 n'
171 65 3 60 1.48519
to r4=-275, r4y"-12, 23, re"-3
0,0, R''-275 Example 8 L d2d3d4n' 171 65 3 60 1.48519
r4x=-6001ray"-10,33,ro"-2
0,0,R"-600Example 9 L dz ds d4n'171
65 3 60 1.48519r4g=-1
500, r4v"-8,0,ro"-12,0,R"-
1500 Example 10 L d 2 d s d 4
n '171 95 3 30 1.48
519r,,=-530,r+y=-7,94,ro=
-20,0, R=-530 Example 11 L d, d, d.

171 95 3 30r4x”
-920yr+y"-7,08,r6"-15,0Example 12 L d, dyu d4 171 95 3 30 r4x"-1400or<y"-6,42,r6"-1
2,01,48519, R=-920 n' 1.48519, R=-1400 Example 13 L d 2 d s d 4
n '171 35 3
90 1.48519r4x"-395,
r4v=-11,02, ro=-20,0, R=-39
5 Example 14 L d z d s d 4
n '171 35 3 90 1.48
5191"4x"-640Hr4f-9-52vro"
-15-0, R=-640 Example 15 L dx (L+ d<'
n'171 35 3 90 1.485
19r4X"-930, r4y"-8,41@re"-
12,0, R”-930 Example 16 L d 2 d s d 4
n171 65 3 60
1.48519r3x”650, r!v”IO,
6tro”ZO,o, R:650 Examples 7 to 16
Figures 14 to 23 show diagrams of the curvature of field for each embodiment, in which the solid line indicates the curvature of field in the sub-scanning direction and the broken line indicates the curvature of field in the main scanning direction.The curvature of field was well corrected in each embodiment. has been done. Also, the linearity corresponding to the fθ characteristic is 9.2z
It is below, and electrical correction is fully possible.

Two comparative examples are listed below.

Comparative Example 2 is an example in which a long cylindrical lens is combined as a correction optical system with the aforementioned optical scanning lens commonly used in Examples 7 to 16, and Comparative Example 3 is an example in which a long cylindrical lens is combined with the optical scanning lens described above, which is commonly used in Examples 7 to 16. This is an example in which a long toroidal lens is combined as a correction optical system. In Comparative Examples 2 and 3, the distance between the long lens that is the correction optical system and the scanned surface is set to 60. In Example 2.3, the radius of curvature of the lens surface on the optical scanning lens side of the correction optical system is r3X in the main scanning direction,
The radius of curvature of the lens surface on the side to be scanned is r4X in the main scanning direction, r4Y in the sub-scanning direction, the wall thickness is dl, and the refractive index is n'.

Comparative example 2 L d 2 d s d 4
n '171 65 3 60 1.4
8519r'3X="+r3y"20.0+r4x"
+r4v=o.

Comparative example 3 L d2ds d4n 171 65 3 60 1.4851
9r3x”150, rxy=20.0.rnyJ50
, r4y=oO Diagrams of field curvature for Comparative Examples 2 and 3 are shown in FIGS. 24 and 25, respectively. In Comparative Example 2,
As shown in FIG. 24, the curvature of field in the sub-scanning direction is significantly under-scanned.Also, in Comparative Example 3, the curvature of field in the sub-scanning direction is slightly corrected compared to Comparative Example 2. There is insufficient correction at intermediate image height.

Embodiments of the claimed optical scanning device will be described below.

Referring to FIG. 3, this figure schematically shows the basic configuration of the claimed optical scanning device. That is, similar to FIG. 1, the optical system arrangement in the optical scanning device is shown expanded along the optical path from the light source to the surface to be scanned.

Figures 3 (I-1) and (II-1) are views of the unfolded state of the optical scanning device viewed from the sub-scanning direction, and in these figures, the vertical direction of the scanned surface 27 is the main scanning direction. be.

3(I-2) and (II-2) are views of the developed state as viewed from the main scanning direction, and in these figures, the vertical direction is the sub-scanning direction.

A light beam from a light source device 21 (LD or LED is assumed in this example as well) is converted into a substantially parallel light beam by a collimating lens 22 as a collimating optical system, and after being shaped into a beam cross section by an aperture 28. , enters the cylindrical lens 23. The cylindrical lens 23 has positive power only in the sub-scanning direction,
Therefore, the light beam is focused only in the sub-scanning direction.

The cylindrical lens 23 has setting conditions such that the light beam focused only in the sub-scanning direction substantially forms a line image at the position of the deflection reflection surface 24, and the longitudinal direction of the line image is in the main scanning direction. This is the corresponding direction. The lens 24 has a beam shaping effect, and may be set so that the image formation position does not coincide with the position of the deflection reflection surface.

Note that the deflection reflection surface 24 is a surface that contributes to the deflection of the light beam among the reflection surfaces of the deflection device, and is also assumed to be a rotating polygon mirror in this embodiment.

The light beam deflected at a constant angular velocity by the deflection device then enters the optical scanning lens 25. The optical scanning lens 25 is a single spherical lens and has a positive refractive index. The light beam transmitted through the optical scanning lens 25 further enters a long troital lens 28A (26B) which is a correction optical system, and after passing through this, enters the scanned surface 27.

The light beam incident on the scanned surface 27 is thus imaged into a spot on the scanned surface 27 by the cooperative action of the optical scanning lens 25 and the long toroidal lens 26^ (26B).

When viewed from the sub-scanning direction, the light beam incident on the optical scanning lens is a parallel light beam, so the optical scanning lens 25 and the long toroidal lens 26A (26B) are positioned at infinity on the object side and at the object side in the main scanning direction. The position of the scanning plane is set to have a geometrically optically substantially conjugate relationship. On the other hand, when viewed from the main scanning direction, the light beam that enters the optical scanning lens 25 is substantially a divergent light beam from a line image located at the position of the deflection reflection surface 24 .

Therefore, the optical scanning lens 25 and the long toroidal lens 2
6A (26B) is such that in the sub-scanning direction, the position of the deflection reflection surface and the position of the surface to be scanned are approximately conjugate in terms of geometrical optics.

Due to this relationship, the so-called "troublesome correction" in the deflection device is performed.

The long toroidal lens 28A (28B) has strong positive refractive power in the sub-scanning direction.

Further, the long toroidal lens 26A (28B) includes an insertion toroidal surface as a concave surface.

Below, the optical scanning lens 25 and the long toroidal lens 26
Example 6 is a specific example of a combination of A (26B).
Give an example.

In either example, the same optical scanning lens 25 is used. The specifications of this optical scanning lens are as follows.

The radius of curvature of the lens surface on the deflection reflection surface side of the optical scanning lens 25 is rl, the radius of curvature of the lens surface on the scanned surface side is rh, the distance between these lens surfaces is dl, and the refractive index of the lens material is nl.
Then, these are given as follows.

1”trz d+n
+-160-60, 291151, 57221 Also, the distance glido between the lens surface on the deflection reflection surface side of this optical scanning lens and the deflection reflection surface is 28.0, and the focal length fi
f=180. Note that the unit of quantity having the dimension of length is 0, and this optical scanning lens has an fθ function.

The following six long lenses can be combined with this optical scanning lens. The distance between the lens surfaces of these long toroidal lenses on the optical scanning lens side, that is, on the deflection reflection surface side, and the lens surface on the long toroidal lens side of the optical scanning lens is d8. The distance between the lens surfaces of the long toroidal lens is d3, and the distance between the lens surface on the scanned surface side and the scanned surface 27 is d.
4. Let n' be the refractive index of the lens material.

According to the above analytical expression, the concave intercalated toroidal surface is rO
and give the value of R.

For surfaces that are not toroidal surfaces, the radius of curvature in the main scanning direction is r. , the radius of curvature in the sub-scanning direction is rn, and when this surface is on the deflection-reflection surface side, the subscript =3. When it is on the side to be scanned, the value is set to 4.

Further, let L be the distance between the deflection reflection surface and the scanned surface.

Further, in each example, the deflection angle is 76 degrees and the effective writing width is about 220+am.

Example 17 L d2da d4n' 208.5 132.5 3.0 30.0 1.
48519r4x r4y l”o
R-900-7, 55-17, 20-900 A diagram of the field curvature due to the combination of this long troital lens and the above-mentioned optical scanning lens is shown in FIG. 26, where the broken line is in the main scanning direction and the solid line is This is field curvature in the sub-scanning direction.

Embodiment 18 An image is formed on the scanned surface 37 by the action of L dv ds d4nxB).

The optical scanning lens 35 is composed of a plurality of lenses and has a positive refractive power, and the long toroidal lens 3flA (38B) has a strong positive refractive power in the sub-scanning direction.

The optical scanning lens 35 further focuses the incident convergent light beam in the direction corresponding to the main scanning.

The long toroidal lens 36A (36B) works together with the optical scanning lens 35 to form an image of the light beam onto the surface to be scanned 37.

Therefore, in the main scanning direction, the optical scanning lens 35 and the long toroidal lens 36A (36B) use the arc-shaped trajectory 39 of the natural focal point Q' as an object surface, and this object surface and the scanned surface. 37 in a geometric-optical conjugate relationship.

Regarding the direction corresponding to the sub-scanning, the optical scanning lens 35 and the long toroidal lens 36A (36B) have a substantially conjugate relationship between the position of the deflection reflection surface 34 and the position of the scanned surface 37 in terms of geometric optics. . This corrects the surface tilt.

Four specific examples are listed below.

In these four embodiments, a common optical scanning lens 35 is used. The specifications of this optical scanning lens are as follows.

The radius of curvature of the i-th lens surface from the deflection-reflecting surface side of the optical scanning lens 35 is rl (i=1 to 4), the distance between the i-th surfaces is d, (i=1 to 3), and the j-th lens surface is When the refractive index of the lens material of the lens is nt (j''1-2), these are given as follows.

i ri dl j n
il-25012,711,511182-24
03,4 3-70018,621,76605 -99 The focal length of this optical scanning lens is f = 143.73 m, and the distance from the deflection reflection surface 34 to the natural focal point Q' @ D
=500■, from the deflection reflecting surface 3 to the first optical scanning lens
The distance d, ) to the surface is 26.0 mm. In addition, the fθ characteristic of the optical scanning lens is 0.5% or less and does not require electrical correction, the deflection angle is 100 degrees, and the effective writing width is 2261 degrees.
It is a super wide-angle lens.

The following examples show the specifications of a long toroidal lens to be combined with the optical scanning lens described above. Barrel-shaped toroidal surfaces are specified by ro and R as an example, and surfaces other than barrel-shaped toroidal surfaces are , the radius of curvature in the main scanning direction is r,
Let the radius of curvature in the sub-scanning direction be rkY, and when this surface is on the deflection/reflection surface side, the subscript is =5, and when it is on the scanned surface side, the subscript is =6.

Further, the distance between the deflection reflection surface and the surface to be scanned is assumed to be L as shown in FIG.

The distance between the lens surfaces of these long toroidal lenses on the optical scanning lens side, that is, the deflection reflection surface side, and the lens surface on the long toroidal lens side of the optical scanning lens is tL,
It is assumed that the distance between the lens surfaces of the long toroidal lens is di, the distance between the lens surface on the surface to be scanned and the surface to be scanned is d, and the refractive index of the lens material is n'.

Example 23 L d4ds di n'168.
5 75.0 3.0 30.0 1.48519
rim rav r(I R150
08,0017,001500 A diagram of the field curvature due to the combination of this long troital lens and the above-mentioned optical scanning lens is shown in FIG. be.

Example 24 L d, dl dl n'1
68.5 45.0 3.0 60. OL4851
9rsy To R700
11,7024,40700 A diagram of the field curvature due to the combination of this long troital lens and the above-mentioned optical scanning lens is shown in FIG. be.

Example 25 L (L ds da n'1
88.5 75.0 3.0 30.0 1.48
519r6 Rrsm rlt -15,40-1000-1000-7,20 A diagram of the curvature of field due to the combination of this long troital lens and the above-mentioned optical scanning lens is shown in FIG. 34, where the broken line indicates the main scanning direction; The solid line represents the curvature of field in the sub-scanning direction.

Example 26 1 d, d, d, n'1
B8.5 45.0 3.0 60.0 1.48
519ro Rr@m r@v -12,85-1500-1500-8,30 The times of field curvature due to the combination of this long troital lens and the above-mentioned optical scanning lens are shown in FIG. The solid line in the main scanning direction is the field curvature in the sub-scanning direction.

Examples 23 and 24 are examples in which the barrel-shaped toroidal surface is directed toward the surface to be scanned (FIG. 4 CI-1) and (1-2)), and examples 25 and 26 are examples in which the barrel-shaped toroidal surface is directed toward the scanned surface. Example facing the scanning lens side (Figure 4 (II-1), (II-2)
).

Good curvature of field is achieved even when the distance between the barrel-shaped toroidal surface and the scanned surface is set to 60+ seconds.

[Effects of the Invention] According to the present invention, a novel scanning optical system and a novel optical scanning device can be provided.

Since these scanning optical systems and scanning optical systems each include a barrel-shaped toroidal surface as a concave surface for correcting field curvature, they can satisfactorily correct field curvature and realize good optical scanning with little variation in spot diameter. In addition, the barrel-shaped toroidal surface is concave and 1
By using a mold with a convex surface that is easy to manufacture, it can be easily molded and can be realized at low cost.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining the invention of claim 2. FIG. 2 is a diagram for explaining the invention of claim 3, FIG. 3 is a diagram for explaining the invention of claim 4, and FIG. 4 is a diagram for explaining the invention of claim 5. . Figure 5 is a diagram for explaining the barrel-shaped toruidal surface;
The figure shows one example of a specific embodiment of the optical scanning device according to the invention of claim 2, FIGS. 7 to 12 are field curvature diagrams regarding the embodiment of claim 2, and FIG. , curvature of field diagrams relating to a comparative example for the invention of claim 2, FIGS. 14 to 23 are curvature of field diagrams relating to the embodiment of the invention of claim 3, and FIGS. 24 and 25 are curvature of field diagrams relating to the embodiment of the invention of claim 3. The curvature of field diagrams, FIGS. 26 to 31, relating to the comparative example are the curvature of field diagrams, FIGS. 32 to 3, relating to the embodiment of claim 4.
FIG. 5 is a curvature of field diagram regarding the embodiment of claim 5. 130. Light source device, 400. Polarized reflective surface, 5009, f
&lens, 6A, 6B, barrel-shaped troital lens,
7. ,,Running diagram Chrysanthemum Zutang Zuyu 5 Figure (1) (II) Figure Figure Figure Figure % Figure (!!!sugar example 4) ('it-equal example 2) (actual example 5) 0 Figure 1 Figure 1 A Figure % A Z Figure (Extreme example 4) Example 5 addressed to the cape) (Actual and example Gn Figure 45 (Comparative example A) % 14 Figure 5 (Figure 5) Figure (%! Sale) Example 7) (Tsu 8 down 6) (Example 9) % 47 Figure Masu B Figure % 9 Figure (Pr N ! I I O) (Example 41) (Tokko fi + 42") % 20 Figure % 2 I Figure % Figure 22 (Example 45) (Fly death example 44) (Flower example 45) Button Figure 26 (Actual sales example (7)) Figure 27 (T sales example J5) % Figure 28 (Tora example/, 9 ) Button 29 figure side 0 figure % 1 figure (actual sale example zo) (actual sale example 24) (actual sale example zz') % z figure (actual sale example 2) Whistle b figure (actual sale example Z4) % U Figure 4 (Sold out example Z) Figure 5 (Sold out example ZCO)

Claims (1)

[Claims] 1. In an optical scanning device that optically scans a surface to be scanned by deflecting a light beam by an optical deflection device, an optical system disposed between the optical deflection device and the surface to be scanned. It has the function of forming an image of the deflected light beam on the surface to be scanned, and also makes the deflection origin of the light beam and the surface to be scanned in a substantially conjugate relationship in terms of geometrical optics in the sub-scanning direction. A scanning optical system comprising, as a concave lens surface, a barrel-shaped toroidal surface whose radius of curvature in the scanning direction becomes smaller as the distance from the optical axis increases in the direction corresponding to main scanning. 2. A light source device that emits a luminous flux, a collimating optical system that converts the luminous flux from this light source device into a substantially parallel luminous flux, and a collimating optical system that converts the luminous flux that has been made into a substantially parallel luminous flux by the collimating optical system into a long line in the direction corresponding to main scanning. A cylindrical lens that forms an image, a deflection device that has a deflection reflecting surface near the imaging position of the line image and deflects the light beam at a constant angular velocity, and a beam deflected by this deflection device that focuses the light beam to be scanned. An optical scanning lens for scanning a surface at approximately constant speed, and working together with this optical scanning lens to substantially form an image of the focused light beam on the surface to be scanned and to form an image in the main and sub-scanning directions. a correction optical system for correcting surface curvature, the optical scanning lens is composed of a plurality of lenses, and the correction optical system is disposed between the optical scanning lens and the surface to be scanned. An optical scanning device comprising a long toroidal lens including, as a concave lens surface, a barrel-shaped toroidal surface whose radius of curvature in the sub-scanning direction becomes smaller as the distance from the optical axis increases in the main-scanning direction. 3. A light source device for emitting a light beam, a focusing optical system for converting the light beam from this light source device into a focused beam, and a focusing optical system for focusing the focused beam by this focusing optical system into a long line image in a direction corresponding to main scanning. A cylindrical lens, a deflection device that has a deflection reflection surface near the imaging position of the line image and deflects the light beam at a constant angular velocity, and further converges the convergent light beam deflected by this deflection device to scan the surface to be scanned. an optical scanning lens for scanning at a substantially constant speed; and working together with the optical scanning lens to substantially form an image of the focused light beam on the surface to be scanned, thereby correcting the surface tilt of the deflection device. and a correction optical system that corrects field curvature in the main and sub-scanning directions, wherein the optical scanning lens is a single lens, and the correction optical system is provided between the optical scanning lens and the scanned surface. What is claimed is: 1. An optical scanning device comprising: a long toroidal lens disposed in a concave lens surface; the concave lens surface includes a barrel-shaped toroidal surface whose radius of curvature in the sub-scanning direction decreases as the radius of curvature in the sub-scanning direction decreases as the distance from the optical axis increases in the main-scanning direction. 4. A light source device that emits a luminous flux, a collimating optical system that converts the luminous flux from this light source device into a substantially parallel luminous flux, and a collimating optical system that converts the luminous flux that has been made into a substantially parallel luminous flux by the collimating optical system into a long line in the direction corresponding to main scanning. A cylindrical lens that forms an image, a deflection device that has a deflection reflecting surface near the imaging position of the line image and deflects the light beam at a constant angular velocity, and a beam deflected by this deflection device that focuses the light beam to be scanned. An optical scanning lens for scanning a surface at approximately constant speed, and working together with this optical scanning lens to substantially form an image of the focused light beam on the surface to be scanned and to form an image in the main and sub-scanning directions. a correction optical system for correcting surface curvature, the optical scanning lens is a single lens, and the correction optical system is a long toroidal lens disposed between the optical scanning lens and the surface to be scanned. An optical scanning device comprising, as a concave lens surface, a barrel-shaped toroidal surface whose radius of curvature in the sub-scanning direction becomes smaller as the distance from the optical axis increases in the main-scanning direction. 5. A light source device that emits a light beam, a focusing optical system that converts the light beam from the light source device into a convergent beam, and a cylindrical lens that forms the converged beam of the convergent optical system into a long line image in the direction corresponding to main scanning. a deflection device that has a deflection reflecting surface near the imaging position of the line image and deflects the light beam at a constant angular velocity; and a deflection device that further focuses the light beam deflected by this deflection device in a direction corresponding to main scanning. an optical scanning lens for scanning the scanning surface at a substantially constant speed; and working together with the optical scanning lens to substantially form an image of the focused light beam on the scanning surface to tilt the surface of the deflection device. and a correction optical system that corrects field curvature in main and sub-scanning directions, and the optical scanning lens is composed of a plurality of lenses, and the optical scanning lens and the optical scanning lens A long toroidal lens disposed between the scanned surface and the concave lens surface, which includes a barrel-shaped toroidal surface whose radius of curvature in the sub-scanning direction becomes smaller as the distance from the optical axis increases in the direction corresponding to the main scanning direction. An optical scanning device.