JP3365855B2 - Scanning optical system - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning optical system, and more particularly to prevention of ghost due to light reflected from the inner surface of the lens surface.

[0002]

2. Description of the Related Art A scanning optical system is indispensable in a laser beam printer, a laser scanner, a bar code reader, etc., and a polygon mirror or a hologram disk is used as an optical deflector. The laser light emitted from the semiconductor laser enters the optical deflector and is scanned,
The scanned light beam is scanned on a surface to be scanned, for example, a photoconductor, via a scanning lens system such as a condenser lens, an imaging lens, and an imaging optical system.

Conventionally, glass has been used for a scanning lens system of such a scanning optical system, and a coating has been applied to prevent reflection. However, recently, for cost reduction,
This scanning lens system is also becoming a synthetic resin, and technically,
Since there are many problems in terms of cost, there is a tendency to omit the antireflection coating. The glass lens with the anti-reflection coating had almost no problem of reflection of laser light, but the plastic lens without the anti-reflection coating had more ghosts due to the reflection between the surfaces than the former, so that the image quality was improved. Will be a factor that adversely affects. The ghost makes the image on the surface to be scanned unclear, and in a laser beam printer, for example, printing becomes unclear. Further, in recent years, since an image having a halftone is expressed, the drum sensitivity tends to be improved, and the deterioration of the image quality due to the ghost cannot be ignored.

[0004]

It is an object of the present invention to provide a scanning optical system which can prevent or reduce the generation of ghosts without using an antireflection coating, based on the above awareness of the problems.
The present invention particularly aims to obtain a scanning optical system capable of effectively preventing a ghost caused by reflection on the inner surface of a lens. Still another object of the present invention is to provide a scanning optical system capable of suppressing a bow (BOW) that may occur as a result of preventing the generation of a ghost. The bow is a phenomenon in which a light beam scanned on a surface to be scanned has an arc shape.

[0005]

SUMMARY OF THE INVENTION The present inventor has found that the cause of a ghost in a scanning optical system of this type can be divided into reflection between a plurality of lenses and reflection inside the lens. The former, that is, the ghost caused by the reflection between multiple lenses, by tilting the lenses,
Can be removed. Generally, the distance between a plurality of lenses in the scanning lens system and the distance between the scanning lens system and the surface to be scanned are large compared to the lens thickness. Can be reached. On the other hand, the reflected light on the inner surface of the lens cannot be sufficiently deflected only by tilting the lens, so that it is difficult to separate the reflected light from the normal light.

According to the present invention, the ghost caused by the light reflected on the inner surface of the lens is shifted in the sub-scanning direction parallel to the optical axis rather than tilting the lens.
It was completed by finding that it can be removed more effectively. Then, in order to more reliably prevent the reflected light from reaching the surface to be scanned, or to obtain a reliable ghost prevention effect with a small amount of lens shift, the light path from the scanning optical system to the surface to be scanned is blocked. It is desirable to provide a member. Further, scan line curvature (bow) caused by shifting the lens is reduced by tilting the lens or by shifting or tilting another correction lens or one lens in a scanning lens system having a plurality of lenses. can do.

More specifically, the present invention is a scanning optical system for scanning a surface to be scanned with a light beam scanned in the main scanning direction by an optical deflector through at least one scanning lens system. Enclose the lens around the gate when molding.
It consists of a plastic lens that exists on one side,
Two, this plastic lens, the sub-scanning direction perpendicular to the optical axis
Shift the gate part away from the optical axis.
It is characterized by having been made. With plastic lens
Is closer to the gate, striae (where the refractive index is non-uniform)
This striae easily affects the imaging system, but
If the gate part of is shifted away from the optical axis,
This adverse effect can be eliminated.

The shifted lens can be tilted about the lens thickness center at the same time to reduce the bow.

The light shielding member for preventing the light reflected by the lens surface of the constituent lens group from reaching the surface to be scanned is provided between the constituent lens groups of the scanning lens system and between the scanning lens system and the surface to be scanned. Can be provided on either one of the above.

The present invention proposes a more specific proposal in a scanning optical system in which the scanning lens system is composed of one imaging lens and one correction lens for correcting the surface tilt of the optical deflector. That is, the imaging lens is shifted in the sub-scanning direction perpendicular to the optical axis , and the correction lens is reflected on the inner surface of the correction lens.
Shifting to deflect from the scanned surface, this
Between the imaging lens and the correction lens, and between the correction lens and the scanned
Internal reflection on the lens surface of the imaging lens, respectively between the surfaces
First and second light blocking to prevent light from reaching the surface to be scanned
It is to arrange the members .

The arrangement position of the first light shielding member in the optical axis direction is
When the height of the reflected light from the optical axis is h ₁₂ , the height of the regular light from the optical axis is h ₀₂ , and the diameter of the regular light in the sub-scanning cross section is φ, | h ₁₂ −h ₀₂ |> φ It is desirable that the position is satisfied.

The present invention further provides a more specific proposal in a scanning optical system in which the scanning lens system is composed of an image forming lens group having a two-lens structure and one correction lens for correcting the surface tilt of the optical deflector. do. That is, the two forming the imaging lens group
Shifting at least one of the lenses in a direction perpendicular to the optical axis, and applying a correction lens to the inner surface of the correction lens.
Shifting the reflection to deflect it from the scanned surface,
Between the imaging lens and the correction lens, and between the correction lens and the correction lens.
Inner surface on the lens surface of the imaging lens, respectively between the scanning surfaces
The first and the second that prevent the reflected light from reaching the surface to be scanned
It is to arrange a light shielding member .

Similarly, the position of the first light blocking member in the optical axis direction is the height from the optical axis of the internally reflected light on the lens surface of the first lens of the imaging lens group to the optical axis h ₁₃ , and the same second lens. Where h _{23 is} the height from the optical axis of the internally reflected light on the lens surface, h _{03 is} the height from the optical axis of the regular light, and φ is the diameter of the regular light in the sub-scanning section, | h ₁₃ − It is preferable to set the position satisfying h ₀₃ |> φ | h ₂₃ −h ₀₃ |> φ.

[0014]

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below with reference to illustrated embodiments. 1 and 2, the scanning lens system 20 includes one imaging lens (fθ lens) 21 and the polarization plane 12 of the optical deflector 12.
FIG. 1 shows a scanning optical system including a correction lens 22 that corrects a surface tilt of R. In FIG.
1 shows a polygon mirror 12 that rotates around 1. As is well known, the laser light emitted from the semiconductor laser 13 is incident on the polygon mirror 12 in a state of being formed into a line image by a collimating lens, a cylindrical lens, etc., and is reflected by each reflection surface 12R on the peripheral surface and scanned. Then, the scanned surface 14 is scanned through the imaging lens 21 and the correction lens 22. The scanned surface 14 is a photosensitive drum in the case of a laser beam printer, for example. A light blocking member 15 that prevents ghost light from reaching the surface to be scanned 14 is disposed between the correction lens 22 of the scanning lens system 20 and the surface to be scanned 14. This light blocking member 15 is used for main scanning (scanning section).
It has a slit 15a extending in the direction, and is arranged at a position that does not block regular light and blocks internally reflected light at the imaging lens 21. The light blocking member 15 can also be configured by a knife edge.

The present invention, by the imaging lens 21 of the scanning lens system 20 is shifted in the vertical sub-scanning Direction and the optical axis, thereby deflecting the ghost light due to internal reflection of the lens, further the light shielding member 15 Is provided to prevent the ghost light from reaching the surface 14 to be scanned. The bow can be suppressed by shifting and tilting the imaging lens 21 at the same time.

FIG. 3 shows an image forming lens 2 of the scanning lens system 20.
1 is shifted by S _{1 in the} direction perpendicular to the optical axis, and θ
FIG. 7 is a diagram for tracing normal light (transmitted light) and light reflected on the inner surface of the imaging lens 21 when tilted by ₁ .
The feature of this trace is that the optical system of internally reflected light that is reflected twice in the lens and then transmitted through the lens is regarded as one single lens, and a paraxial amount is given.

In the figure, e _to ; the distance in the optical axis direction between the incident point on the imaging lens 21 and the first principal point of the normal light (transmitted light) of the first lens, e _r0 ; the imaging lens 21 In the optical axis direction between the point of incidence on the first lens and the first principal point of the internally reflected light of the first lens, _et1 ; between the second principal point of the regular light (transmitted light) of the first lens and the light shielding member , E _r1 ; distance between the second principal point of the inner surface reflected light of the first lens and the light blocking member, dat ₁ ; from the lens thickness center of the first lens transmitted light to the first principal point of the first lens intervals, dar _1; distance from the lens thickness of the first lens internally reflected light up to the first principal point of the first lens, dbt _1; first lens second principal point of the lens center thickness of the first lens transmitted light Distance up to dbr ₁ ; 1st lens from the center of the lens thickness of the light reflected on the inner surface to the 1st
The distance to the second principal point of the lens, f _t1, the focal length of the transmitted light of the first lens, f _r1 ; the focal length of the reflected light on the inner surface of the first lens, and the regular light (printing light) from the imaging lens 21. The exit angle (rad.) U ₀₁ , the height h _{01 of} the same ray of light incident on the imaging lens 21, and the height h of the ray after exiting from the imaging lens 21.
₀₂ is given by the following equations. u ₀₀ is the incident angle of the incident light to the optical system, h ₀₀ is the incident height of the incident light to the optical system, and generally u ₀₀ = 0 and h ₀₀ = 0.

[0019] _{u 01 = u 00 + (h} 01 -S 1 + dat 1 · θ 1) / f t1 h 01 = h 00 -u 00 · e t0 h 02 = h 01 - (dbt 1 -dat 1) · θ ₁ -u ₀₁ · e _t1

Further, the angle of emission (rad.) Of the internal reflection light (ghost light) from the imaging lens 21 from the imaging lens 21.
u ₁₁ , the height h ₁₁ of incident light of the same ray on the imaging lens 21, and the height h ₁₂ of light ray after exiting from the imaging lens 21 are respectively given by the following equations.

[0021] _{u 11 = u 00 + (h} 11 -S 1 + dar 1 · θ 1) / f r1 h 11 = h 00 -u 00 · e r0 h 12 = h 11 - (dbr 1 -dar 1) · θ _2- u ₁₁ · e _r1

Assuming that the diameter of the normal light in the sub-scan section is φ, the light shielding member 15 may be arranged at a position satisfying | h ₁₂ −h ₀₂ |> φ with these parameters.

In FIG. 4, the scanning lens system 20 includes an imaging lens group (fθ lens) 21 having a two-element structure including a first imaging lens 21a and a second imaging lens 21b, and a polarization plane 1 of the optical deflector 12.
If made of the correcting lens 22 for correcting the tilt of the 2R, S ₁ of the first lens 21a in the vertical sub-scanning Direction and the optical axis
With shifting, is tilted by theta _1, with to S ₂ shifts the second lens 21b in a direction perpendicular to the optical axis, normal light when allowed to tilt by theta ₂ and (transmitted light) the first lens 21a, second It is a figure for tracing the inner surface reflected light in lens 21b. Similar to FIG. 3, the feature of this trace is that the optical system of internally reflected light that is reflected twice in the lens and then transmitted through the lens is regarded as one single lens, and a paraxial amount is given.

In the figure, e ₀₀ ; the point of incidence on the first lens 21a and the first lens 21a
Of the normal light (transmitted light) with respect to the first principal point in the optical axis direction, e ₀₁ ; the point of incidence on the first lens 21a and the first lens 21a
The optical axis distance between the first principal point of the inner surface reflected light and _e02 ; the point of incidence on the first lens 21a and the first lens 21a
Of the normal light (transmitted light) of the first lens 21a in the optical axis direction, e ₁₀ ; the second principal point of the normal light (transmitted light) of the first lens 21a and the normal light of the second lens 29b (transmitted light); Optical distance in the optical axis direction from the first principal point, e ₁₁ ; the second principal point and the second principal point of the inner surface reflected light of the first lens 21 a.
Regular light lens 29b in the optical axis direction distance between the first principal point of the (transmitted light), e _12; internal reflection of the normal light second principal point and the second lens 29b of the (transmitted light) of the first lens 21a Optical axis direction distance from the first principal point of light, e ₂₀ ; Optical axis direction distance between the second principal point of the normal light (transmitted light) of the second lens 29 b and the light shielding member, e ₂₁ ; The distance in the optical axis direction between the second principal point of the normal light (transmitted light) of the second lens 29b and the light shielding member, e ₂₂ ; between the second principal point of the inner surface reflected light of the second lens 29b and the light shielding member Optical axis direction distance, dat _n ; distance from the lens thickness center of the nth lens transmitted light to the first principal point, dar _n ; first from the lens thickness center of the nth lens inner surface reflected light
Distance to principal point, dbt _n ; Distance from lens thickness center of nth lens transmitted light to second principal point, dbr _n ; Distance from lens thickness center of nth lens internal reflection light to 2nd
The distance to the principal point, ft _n ; focal length of light transmitted through the n-th lens, fr _n ; focal length of reflected light on the inner surface of the n-th lens, are the first lens 21a and the second lens of normal light (printing light).
The exit angles (rad.) U ₀₁ , u ₀₁₂ from the lens 21b, the incident light height h ₀₁ of the same ray on the first lens 21a, the second lens 2
The height h ₀₂ of the incident light on 1b and the height h ₀₃ of the light ray after being emitted from the second lens 21b are respectively given by the following equations.

[0025] _{u 01 = u 00 + (h} 01 -S 1 + dat 1 · θ 1) / f t1 u 02 = u 01 + (h 02 -S 2 + dat 2 · θ 2) / f t2 h 01 = h 00 −u ₀₀ · e ₀₀ h ₀₂ = h ₀₁ − (dbt ₁ −dat ₁ ) · θ ₁ −u ₀₁ · e ₀₁ h ₀₃ = h ₀₂ − (dbt ₂ −dat ₂ ) · θ ₂ −u ₀₂ · e ₀₂

Further, the first lens 21a and the second lens 21b of the internal reflection light (ghost light) on the first lens 21a.
Emission angles (rad.) U ₁₁ , u ₁₂ , incident light height h ₁₁ of the same ray on the first lens 21a, incident light height h ₁₂ on the second lens 21b, and emission from the second lens 21b The height h ₁₃ from the subsequent optical axis is given by the following equations, respectively.

U ₁₁ = u ₀₀ + (h ₁₁ −S ₁ + dar ₁ · θ ₁ ) / f _r1 u ₁₂ = u ₁₁ + (h ₁₂ −S ₂ + dat ₂ · θ ₂ ) / f _t2 h ₁₁ = h ₀₀ −u ₀₀ e ₁₀ h ₁₂ = h ₁₁ − (dbr ₁ −dar ₁ ) · θ ₁ −u ₁₁ · e ₁₁ h ₁₃ = h ₁₂ − (dbt ₂ −dat ₂ ) · θ ₂ −u ₁₂ · e ₁₂

Further, the first lens 21a and the second lens 21b of the internal reflection light (ghost light) on the second lens 21b.
The emission angles (rad.) U ₂₁ and u ₂₂ , the incident light height h ₂₁ of the same light ray on the first lens 21a, the incident light height h ₂₂ on the second lens 21b, and the emission light from the second lens 21b the height h ₂₃ from the optical axis of the are given by the following equation.

[0029] _{u 21 = u 00 + (h} 21 -S 1 + dat 1 · θ 1) / f t1 u 22 = u 21 + (h 22 -S 2 + dar 2 · θ 2) / f r2 h 21 = h 00 −u ₀₀ · e ₂₀ h ₂₂ = h ₂₁ − (dbt ₁ −dat ₁ ) · θ ₁ −u ₂₁ · e ₂₁ h ₂₃ = h ₂₂ − (dbr ₂ −dar ₂ ) · θ ₂ −u ₂₂ · e ₂₂

Assuming that the diameter of the normal light in the sub-scanning section is φ, in this case, the light shielding member 15 satisfies | h ₁₃ −h ₀₃ |> φ | h ₂₃ −h ₀₃ |> φ with these parameters. It is better to place it in the position where

Next, the present invention will be described with reference to specific numerical examples. Example 1 FIGS. 5 to 10 show the application of the present invention to a scanning lens system 20 including one imaging lens 21 and one correction lens 22 as shown in FIGS. 1 to 3. is there. 5 and 6 show the optical path of the regular light, and FIGS. 7 and 9 show the optical path of the internally reflected light at the imaging lens 21. 8 and 10
FIG. 10 is a partially enlarged view of FIGS. 7 and 9, respectively. 7,
The shaded portions in FIGS. 9 and 11 indicate the ghost light cut portion. Table 1 shows numerical data of this lens system.

In the table, F _NO. Is the F number, f is the focal length,
w is a half angle of view, R is the radius of curvature of each surface of the lens in the main scanning plane, R _Z is the radius of curvature in the sub-scanning section, D is the lens thickness or lens interval, and N is the refractive index for the d-line.

[0033]

[Table 1] f = 180.0 F _NO. = 70 w = 34.38 ° surface No. RR _Z DN 40.00 1 * 2049.31 14.00 1.48617 2 -89.55 100.00 Shading member 5.0 3 -744.00 26.25 5.0 1.48617 4 * -1093.55 69.27 * is an aspherical surface No.1; K = -0.4606, A4 = -2.99513 x 10 ^-7 , A6 = 1.06203 x 10
^-10 , A8 = -1.90963 × 10 ^-14 No.2; K = -0.5130, A4 = -5.97983 × 10 ^-8 , A6 = 1.25074 × 10
^-12 However, the aspherical surface is defined by the following equation. x = cy ² / {1+ [1- (1 + K) c ² y ² ] ^1/2 } + A4y ⁴ + A6y ⁶ + A8y ⁸

First lens shift amount 1.00 mm First lens tilt amount 0.4 ° Shading member height 2.0 Printing light diameter on the light blocking member (sub-scan section) 1.05

The bow (maximum value of deviation from the reference scanning plane) in this embodiment is 0.036 mm, which is sufficiently suppressed. No ghost was found on the surface 14 to be scanned.

In FIG. 11, the correction lens 22 is shifted in order to reduce the internal reflection of the correction lens.
An example in which the second light shielding member 16 is arranged between the correction lens 22 and the surface to be scanned 14 is shown. Figure 12
FIG. 12 is a partially enlarged view of FIG. 11. In this embodiment, the shift amount of the correction lens 22 is −0.2 mm, and the generated bow is 0.049. According to this embodiment, it is possible to reduce the ghost caused by the correction lens 22.

Table 2 shows various data corresponding to FIG. 3 of the above lens system. However, u ₀₀ and h ₀₀ are both zero.

[Table 2] First lens transmitted (normal) light First lens inner surface reflected light f _t1 ; 176.862 f _r1 ; 27.548 dat ₁ ; 2.045 dar ₂ ; 5.562 dbt ₁ ; 6.605 dbr ₂ ; -10.630 e ₀₁ ; 100.395 e ₁₁ ; 117.630 S ₁ ; 1.0 S ₁ ; 1.0 θ ₁ ; 0.4 ° θ ₁ ; 0.4 ° u ₀₁ ; -5.573 × 10 ^-3 u ₁₁ ; -3.489 × 10 ^-2 h ₀₁ ; 0 h ₁₁ ; 0 Transmission on the light shielding member ( Regular light) Light reflected on the inner surface of the first lens h ₀₂ ; 0.528 h ₁₂ ; 4.217 However, the light blocking member 15 is located 100 mm from the imaging lens 21.

[Embodiment 2] FIG. 13 to FIG.
As described above, the present invention is applied to the scanning lens system 20 including the imaging lens group 21 having the two lenses of the first lens 21a and the second lens 21b, and the correction lens 22. Figure 1
3 and 14 show the optical path of the regular light, and FIGS.
Shows the optical path of the internal reflection light at the first lens 21a, and FIGS. 19 and 21 show the optical path of the internal reflection light at the second lens 21b. 16 and 18 are respectively shown in FIG.
5 and FIG. 17 are partially enlarged views, and FIGS. 20 and 22 are partially enlarged views of FIG. 19 and FIG. 21, respectively. 15,
The shaded area in FIGS. 17, 19 and 21 is the ghost light cutting section. Table 3 shows numerical data of this lens system.

[0039]

[Table 3] f = 135.5 F _NO. = 50 w = 45.67 ° Surface No. RR _Z DN 37.00 1 * 2822.00 15.60 1.48617 2 -105.00 2.00 3 -270.00 23.7 13.30 1.48617 4 -107.00 63.00 Slit 1.50 5 -711.00 5.00 1.48617 6 -623.00 62.14 * is aspherical No.1; k = 4.12, A4 = -9.20 × 10 ^-8 , A6 = 2.77 × 10 ^-11 , A8 =
-3.16 x 10 ^-15

First lens 21a shift amount −1.4 mm First lens 21a tilt amount −1.2 ° Second lens 21b shift amount 1.5 mm Second lens 21b tilt amount 0 ° Light blocking member 15 aperture size shift −0. 1, short width
1.8 mm Regular light diameter on the light shielding member (sub-scan section) 1.29

The bow of this example is 0.107 mm, which is sufficiently suppressed. No ghost was found on the surface 14 to be scanned.

Tables 4 and 5 show various data of the above lens system corresponding to FIG. However, u ₀₀ and h ₀₀ are both zero.

[0043]

TABLE 4 first lens 21a transmission (normal) light first lens internally reflected light second lens internally reflected light _{f t1; 208.591 f r1; 32.270} f t1; 208.591 dat 1; 2.338 dar 1; 6.14 dat 1; 2.338 dbt ₁ ; 7.423 dbdar ₁ ; -11.768 dbt ₁ ; 7.423 e ₀₁ ; 16.815 e ₁₁ ; 36.006 e ₂₁ ; 11.324 S ₁ ; -1.4 S ₁ ; -1.4 S ₁ ; -1.4 θ ₁ ; -1.2 ° θ ₁ ; -1.2 ° θ ₁ ; -1.2 ° u ₀₁ ; 6.946E-03 (rad) u ₁₁ ; 4.737 × 10 ^-2 u ₂₁ ; 6.946 × 10 ^-3 h ₀₁ ; 0 h ₁₁ ; 0 h ₂₁ ; 0

[0044]

[Table 5] Second lens 21b Transmitted (normal) light First lens inner surface reflected light Second lens inner surface reflected light f _t2 ; 355.085 f _t2 ; 355.085 f _r2 ; 48.403 dat ₂ ; 7.788 dat ₂ ; 7.788 dat ₂ ; 2.297 dbt ₂ ; 12.372 dbt ₂ ; 12.372 dbt ₂ ; -11.746 e ₀₂ ; 57.278 e ₁₂ ; 57.278 e ₂₂ ; 81.396 S ₂ ; 1.5 S ₂ ; 1.5 S ₂ ; 1.5 θ ₂ ; 0 ° θ ₂ ; 0 ° θ ₂ ; 0 ° u ₀₂ ; 2.094E-03 (rad) u ₁₂ ; 3.940 × 10 ^-2 u ₂₂ ; -2.787 × 10 ^-2 h ₀₂ ; -0.223 h ₁₂ ; -1.330 h ₂₂ ; -0.185 Transmission on light shielding member (regular) Light First lens inner surface reflected light Second lens inner surface reflected light h ₀₃ ; -0.103 (-0.131) h ₁₃ ; -3.586 (-3.522) h ₂₃ ; 2.083 (1.973) The light shielding member is located 63 mm from L2. ()
The inside is the ray tracing result, and the difference from the result by the above calculation formula is very small.

[Embodiment 3] In Embodiment 3, the same lens configuration as that of Embodiment 2 is used, but the shift amount and tilt amount of the first lens 21a and the second lens 21b are changed.
Table 6 shows the data of the shift amount and the tilt amount. Figure 2
3 and FIG. 24 show this lens system. FIG. 25 shows
FIG. 25 is a partially enlarged view of FIG. 24. The shaded portion in FIG. 24 is the ghost light cut portion.

[0046]

[Table 6] First lens 21a shift amount-1.0 mm Tilt amount of first lens 21a −1.0 ° Second lens 21b shift amount 1.0 mm Second lens 21b tilt amount 1.0 ° Correction lens 22 shift amount 0.6 mm

The bow of this example is 0.044 mm, which is sufficiently reduced. It was also confirmed that no ghost was generated on the scanned surface 14.

[0048]

According to the scanning optical system of the present invention, the scanning lens system has a simple structure in which at least one lens of the scanning lens system is shifted in the direction perpendicular to the optical axis. Even when the lens is used, it is possible to prevent the occurrence of ghost. By disposing the light-shielding member at a predetermined position, it is possible to more reliably prevent the occurrence of ghost, and by tilting the lens, it is possible to suppress the bow that occurs as a result of the shift.

[Brief description of drawings]

FIG. 1 is a plan view showing a first embodiment of a scanning optical system according to the present invention.

FIG. 2 is a front view of FIG.

FIG. 3 is a diagram for tracking the regular light and the internally reflected light when one imaging lens is shifted and tilted in the scanning optical system of FIGS. 1 and 2.

FIG. 4 shows a case where the image forming lens group includes two lenses,
It is a figure for tracking the regular light and the inner surface reflected light when each of the two imaging lenses is shifted and tilted.

FIG. 5 is a plan view showing an optical path of regular light, showing a first specific example of the scanning optical system according to the present invention.

FIG. 6 is a front view of FIG.

7 is a plan view showing an optical path of light reflected on the inner surface of the imaging lens in the scanning optical system of FIG.

FIG. 8 is a partially enlarged view of FIG.

9 is a front view of FIG. 7. FIG.

FIG. 10 is a partially enlarged view of FIG.

FIG. 11 is a plan view showing an example in which the correction lens is further shifted and a light shielding member is arranged between the correction lens and the surface to be scanned in the scanning optical system of FIGS.

FIG. 12 is a partially enlarged view of FIG.

FIG. 13 is a plan view showing an optical path of regular light, showing a second specific example of the scanning optical system according to the present invention.

FIG. 14 is a front view of FIG.

FIG. 15 is a plan view showing the optical path of the internally reflected light of the first lens of the imaging lens group in the scanning optical system of FIG.

16 is a partially enlarged view of FIG.

FIG. 17 is a front view of FIG. 15.

FIG. 18 is a partially enlarged view of FIG.

FIG. 19 is a plan view showing the optical path of the inner surface reflected light of the second lens of the imaging lens group in the scanning optical system of FIG.

FIG. 20 is a partially enlarged view of FIG.

FIG. 21 is a front view of FIG.

22 is a partially enlarged view of FIG. 21. FIG.

23 is a front view showing an optical path of regular light in an example in which the correction lens is further shifted and a light shielding member is arranged between the correction lens and the surface to be scanned in the scanning optical system of FIGS. is there.

FIG. 24 is a front view showing a state where the internal reflection light generated by the correction lens is blocked by a light blocking member.

FIG. 25 is a partially enlarged view of FIG. 24.

[Explanation of symbols]

12 Polygon mirror (deflector) 13 Semiconductor laser 14 Scanned surface 15 Light-shielding member 16 Second light shielding member 20 scanning lens system 21 Imaging lens (group) 21a First imaging lens 21b Second imaging lens 22 Correction lens

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G02B 26/10

Claims (7)

(57) [Claims] 1. A scanning optical system in which a light beam scanned by an optical deflector in a main scanning direction is scanned on a surface to be scanned via a scanning lens system, and at least one lens of the scanning lens system is formed at the time of molding.
Plastic lens with the gate part of the peripheral part
And this plastic lens as the optical axis
In the vertical sub-scanning direction, the gate portion is
Scanning optics characterized by shifting away
system. 2. The scanning optical system according to claim 1, wherein the shifted lens is simultaneously given a tilt centered on a lens thickness center. 3. The scanning optical system according to claim 1, wherein the scanning lens system is configured between lens groups, or between the scanning lens system and a surface to be scanned. Further, a scanning optical system in which a light shielding member which is parallel to the main scanning direction and which prevents reflected light on the lens surfaces of the constituent lens groups from reaching the surface to be scanned is provided. 4. A scanning optical system in which a light beam scanned in a main scanning direction by an optical deflector is scanned on a surface to be scanned through a scanning lens system, wherein the scanning lens system includes one imaging lens. The image forming lens is shifted in the sub-scanning direction perpendicular to the optical axis , and the correcting lens is an inner surface reflection of the correcting lens. The surface to be scanned
Are shifted in order to deflect from the image forming lens and the correction lens, and between the correction lens and the correction lens.
Inner surface on the lens surface of the imaging lens, respectively between the scanning surfaces
The first and the second that prevent the reflected light from reaching the surface to be scanned
A scanning optical system in which a light shielding member is arranged. 5. The scanning optical system according to claim 4, above
The first light-shielding member has a height h ₁₂ from the optical axis of the reflected light that exits the imaging lens, a height h ₀₂ from the optical axis of the regular light, and a diameter of the regular light in the sub-scanning section. Where φ is φ, a scanning optical system arranged at a position satisfying | h ₁₂ −h ₀₂ |> φ. 6. A scanning optical system in which a light beam scanned by an optical deflector in a main scanning direction is scanned on a surface to be scanned through a scanning lens system, wherein the scanning lens system comprises a two-lens imaging lens group. And one correction lens for correcting the surface tilt of the optical deflector, and at least one of the two lenses forming the imaging lens group is shifted in the sub-scanning direction perpendicular to the optical axis. In the correction lens, the internal reflection of the correction lens causes the surface to be scanned to
Are shifted in order to deflect from the image forming lens and the correction lens, and between the correction lens and the correction lens.
Inner surface on the lens surface of the imaging lens, respectively between the scanning surfaces
The first and the second that prevent the reflected light from reaching the surface to be scanned
A scanning optical system in which a light shielding member is arranged. 7. The scanning optical system according to claim 6, above
Note that the first light shielding member has a height h from the optical axis of the light internally reflected by the first lens of the imaging lens group after being emitted from the first lens.
₁₃ , the height of the internally reflected light from the second lens from the optical axis after exiting the second lens is h ₂₃ , the height of the regular light from the optical axis is h ₀₃ , and the sub-scan section of the regular light The scanning optical system is arranged at a position satisfying | h ₁₃ −h ₀₃ |> φ | h ₂₃ −h ₀₃ |> φ, where φ is the diameter at.