JPH1114932A - Scanning optical system and optical scanning device - Google Patents

Abstract

(57) [Summary] To effectively correct inherent scan line bending caused by the design of an optical scanning device. A luminous flux from a light source is incident on a deflecting / reflecting surface of an optical deflector from a direction obliquely intersecting a rotation axis of the deflecting / reflecting surface, and is deflected at a constant angular velocity.
The deflected light beam is condensed as a light spot on the surface to be scanned 50, and optical scanning is performed symmetrically with respect to a plane PL including the direction of incidence of the light beam from the light source 10 on the deflective reflection surface 31 and the rotation axis 30Ax. In the optical scanning device, a scanning image forming optical system 41 for condensing a light beam from the light source 10 side as a light spot on the surface 50 to be scanned, and is configured to have one or more lenses. Has a correction refraction surface 41B for correcting the bending of the scanning line.
1B, the intrinsic inclination β ₄₁ in the sub-scan section at the incident position of the deflected light beam on the correction refraction surface 41B is determined according to the incident position so as to correct the scan line bending inherent to the optical scanning device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a scanning image forming optical system and an optical scanning device.

[0002]

2. Description of the Related Art An optical scanning apparatus which deflects a light beam from a light source side at an equal angular velocity by an optical deflector and condenses the deflected light beam as a light spot on a surface to be scanned and performs optical scanning is related to various printers. It is widely known. Conventionally, such an optical scanning device is generally configured such that an optical arrangement is such that a light beam from a light source side and a surface on which a deflecting light beam deflects and sweeps are on the same plane. Has the following problems.

[0003] First, the "floor area of the optical scanning device" becomes large. Secondly, a rotating polygon mirror is most commonly used as an optical deflector. However, since the rotation axis of the rotating polygon mirror is far from the deflecting / reflecting surface, the incident position of the light beam from the light source side to the deflecting / reflecting surface is reduced. So-called "sag", which is displaced with respect to the deflecting reflection surface with the rotation of the deflecting reflection surface, and the starting point of deflection of the deflected light beam is changed
Is generated, but the angle between the direction of the deflecting light beam that realizes the image height of the light spot: 0 and the direction of the incident light beam from the light source side to the deflecting / reflecting surface, which is the reference for optical scanning, is, for example, about 60 degrees. Therefore, the sag is asymmetrically generated on both sides of the image height: 0 in the optical scanning area. For good optical scanning, the curvature of field and “constant velocity characteristics such as fθ characteristics” are asymmetrically generated. It becomes necessary to make corrections accordingly, and it becomes difficult to design a scanning imaging optical system.

As an optical arrangement capable of solving such a problem at once, a light beam from a light source is incident on a deflecting / reflecting surface of an optical deflector from a direction obliquely intersecting the rotation axis of the deflecting / reflecting surface, thereby achieving a uniform angular velocity. To converge the deflected light beam as a light spot on the surface to be scanned, and perform optical scanning symmetrically with respect to a plane including the incident direction from the light source side to the deflective reflection surface and the rotation axis. Optical arrangements are conceivable.

In this way, the optical system from the light source to the optical deflector and the optical system after the optical deflector can be laid out so as to be vertically overlapped. The size of the scanning device can be reduced. Further, since optical scanning is performed symmetrically with respect to a plane including the direction of incidence from the light source side to the deflecting reflection surface and the rotation axis, even if sag occurs, it occurs symmetrically at an image height of 0. Therefore, it is easy to correct the constant velocity characteristics and the curvature of field.

However, such an optical arrangement has the following problems. That is, in order to make the light beam from the light source incident on the deflecting reflection surface of the optical deflector so as to obliquely intersect with the rotation axis of the deflecting reflection surface, the deflecting light beam is deflected so as to sweep the conical surface. The “position where the light beam enters the optical system thereafter” fluctuates to a considerable extent in the sub-scanning corresponding direction (the direction corresponding to the sub-scanning direction on the optical path from the light source to the surface to be scanned) due to the deflection. Therefore, the trajectory of the light spot on the surface to be scanned does not become a straight line, and so-called "scanning line bending" occurs.

The light beam from the light source is converted into a long line image in the main scanning direction (a direction corresponding to the main scanning direction on the optical path from the light source to the surface to be scanned) near the deflecting reflection surface of the optical deflector. It is possible to make the imaging optical system for “anamorphic optical system with different powers in the main and sub-scanning corresponding directions” and to make the position of the deflecting reflective surface and the position of the scanned surface “substantially conjugate in the sub-scanning corresponding direction”. , Is widely used as a method for correcting the "surface tilt of the deflecting reflection surface" in the optical deflector,
If the conjugate relationship is perfect, the scanning line bending will be automatically corrected.However, the "fluctuation of the deflected light beam in the sub-scanning corresponding direction" in the case of surface tilt correction may be very small. It is a premise, as described above, it is difficult to correct the "large scanning line bending caused by the deflection of the deflected light beam to sweep the conical surface" by the above "conjugate relationship", and such a correction is forcibly performed. Attempting to do so may sacrifice other optical performance required of the scanning imaging optical system, such as field curvature.

[0008]

According to the present invention, a light beam from a light source is incident on a deflecting / reflecting surface of an optical deflector from a direction obliquely intersecting the rotation axis of the deflecting / reflecting surface and is deflected at a uniform angular velocity. An optical scanning device that converges a deflected light beam as a light spot on a surface to be scanned and performs optical scanning symmetrically with respect to a plane including the direction of incidence from the light source side to the deflective reflection surface and the rotation axis. It is another object of the present invention to effectively correct the above-mentioned scanning line bending.

[0009]

The scanning image forming optical system according to the present invention is arranged such that a light beam from a light source is incident on a deflecting / reflecting surface of an optical deflector from a direction obliquely intersecting the rotation axis of the deflecting / reflecting surface. It is deflected at a constant angular velocity, the deflected light beam is condensed as a light spot on the surface to be scanned, and symmetrically with respect to a plane including the incident direction of the light beam from the light source side to the deflective reflection surface and the rotation axis. In a light scanning device that performs light scanning, a scanning image forming optical system that condenses a light beam from a light source side as a light spot on a surface to be scanned ”.

[0010] The scanning image forming optical system according to the first aspect of the present invention comprises: "One or more lenses, and at least one surface of the lens has a correction refracting surface for correcting a bending of a scanning line. The correction refraction surface is determined in accordance with the incident position so that the inherent inclination in the sub-scanning cross section at the incident position of the deflected light beam on the correction refraction surface corrects the scan line bending unique to the optical scanning device. Be ".

The above-mentioned "incident light beam from the light source side is incident on the deflecting and reflecting surface of the optical deflector from a direction obliquely intersecting with the rotation axis of the deflecting and reflecting surface" means that the principal ray of the light beam incident from the light source side is The rotation axis of the deflecting reflection surface is included in the “same plane”, which means that the principal ray forms an “angle that is not a right angle” with the rotation axis. The angle formed by the principal ray and the rotation axis is determined according to the optical arrangement of the optical scanning device, but is suitably "about 70 to 89 degrees".

As the "optical deflector", a rotating polygon mirror, a rotating single mirror or a rotating two-face mirror can be used. When the optical deflector is a rotating polygon mirror, the rotation axis of the deflecting / reflecting surface is separated from the deflecting / reflecting surface. There can be.

"The scanning image forming optical system focuses the light beam from the light source side as a light spot on the surface to be scanned" means that the function of the scanning image forming optical system is the light beam immediately before entering the optical deflector. And the case of acting on the deflected light beam, and the case of acting only on the deflected light beam.

Japanese Patent Application Laid-Open No. 6-75162 discloses a "rotating lens mirror" which is integrated with a deflecting / reflecting surface and has a refracting surface having an incident surface on the deflecting / reflecting surface and an exit surface from which the reflected light beam exits. The function of such a rotary lens mirror is "to act on the light beam immediately before entering the optical deflector and the deflected light beam". The "scanning optical system" in the present invention can be constituted by such a rotating lens mirror, or can be constituted by including the rotating lens mirror. A “surface” can be a “correcting refractive surface”.

The correction refracting surface may be formed as one surface of a lens included in the scanning image forming optical system, or may be formed as two or more surfaces, and a desired effect is obtained by combining the correction effects of the two or more surfaces. May be realized.

The "sub-scanning section" means a plane section orthogonal to the main scanning direction with respect to the lens located closer to the surface to be scanned than the optical deflector. Further, when the scanning image forming optical system is the rotating lens mirror, or when the rotating lens mirror is included in the scanning image forming optical system, with respect to the incident surface of the rotating lens mirror, the principal ray of the incident light flux from the light source side and A plane section parallel to the sub-scanning corresponding direction is defined as a sub-scanning section, and an exit side surface is defined as a plane section parallel to the principal ray of the emitted light beam and the sub-scanning corresponding direction.

The “scanning line bending inherent to the optical scanning device” occurs in the design when an optical scanning device is designed without the scanning image forming optical system having the “scanning line bending correction function by the correction refraction surface”. Scan line bend. That is, the scanning line bending inherent to the optical scanning device is determined by the design of the optical scanning device, and therefore, a correction refraction surface that corrects such a scanning line bending can be determined by design. .

According to the first aspect of the present invention, the scanning image forming optical system is constituted by a "single lens" and can be disposed between the optical deflector and the surface to be scanned (claim 2). In this case, the correction refraction surface can be one surface and / or the other surface of a single lens that forms the scanning imaging optical system.

In the scanning image forming optical system according to claim 1 or 2, the correction refracting surface can be formed as "the lens surface of the scanning image forming optical system which is closest to the surface to be scanned". ). In this case, since there is no refraction surface on the optical path on the scanning surface side with respect to the correction refraction surface, the design of the correction refraction surface becomes easy.

In the optical scanning device, it is necessary to make each dot by optical writing have an equal interval in the main scanning direction as much as possible. To realize this, the timing for modulating the deflection light beam is electrically controlled. An adjustment method, a method of setting optical characteristics (fθ characteristics, etc.) of the scanning imaging optical system itself so that optical scanning is performed at a constant speed, or a common use of the above-described electrical correction and optical correction There is a way to do that. It is difficult to perform high-speed constant-velocity correction by electrical adjustment, and when high quality is required for recorded images, the scanning imaging optical system can perform “optical scanning with a deflected light beam deflected at a constant angular velocity. It is preferable to have a function of converting into (a fourth aspect).

As described above, a rotary single-sided mirror can be used as the optical deflector, and such an optical deflector does not have "the surface tilt of the deflecting and reflecting surface as in a rotary polygonal mirror".
Therefore, it is not necessary to provide a surface tilt correction function. However, when an optical deflector having a plurality of deflecting and reflecting surfaces, such as a rotary polygon mirror, is used, a function for correcting the surface tilt is required. The scanning image forming optical system according to the present invention can have a function of “making the vicinity of the starting point of deflection by the optical deflector and the position of the surface to be scanned substantially geometrically conjugate in the sub-scanning corresponding direction”. 5) By doing so, "surface tilt" of the deflecting / reflecting surface in the optical deflector can be corrected. If this function is thoroughly implemented, as described above, "scanning line bending" will not occur, but in practice, it is assumed that the constant velocity characteristics, field curvature, etc. are favorably corrected. Originally, it is difficult to completely realize the conjugate relationship. Here, the conjugate relationship is realized in consideration of the optical characteristics required for the scanning imaging optical system, and means a conjugate relationship that can correct surface tilt.

According to a sixth aspect of the present invention, there is provided an optical scanning apparatus comprising the steps of: "deflecting a light beam from a light source side into a deflecting / reflecting surface of an optical deflector in a direction obliquely intersecting with the rotation axis of the deflecting / reflecting surface; An optical scanning device that converges a deflected light beam as a light spot on a surface to be scanned and performs optical scanning symmetrically with respect to a plane including the direction of incidence of the light beam from the light source side on the deflecting reflection surface and the rotation axis. ", Wherein the scanning imaging optical system according to any one of claims 1 to 4 is used.

According to a seventh aspect of the present invention, there is provided an optical scanning apparatus comprising: "a light beam from a light source is made to enter a deflecting reflection surface of a rotary polygon mirror which is an optical deflector from a direction obliquely intersecting a rotation axis of the rotary polygon mirror; A linear image is formed in the vicinity of the deflecting reflection surface as a long line image in the main scanning direction, and the image is deflected at a constant angular velocity by a rotating polygon mirror, and the deflected light beam is condensed as a light spot on the surface to be scanned. An optical scanning device that performs optical scanning symmetrically with respect to a plane including the incident direction and the rotation axis ”, wherein the scanning image forming optical system according to claim 5 is used. Of course, it is needless to say that the scanning image forming optical system can be provided with a function of equalizing the speed to realize the constant speed optical scanning.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram for explaining a scanning image forming optical system and an optical scanning device according to an embodiment of the present invention. FIG. 1A shows “a state in which the optical arrangement from the light source to the surface to be scanned is viewed from the main scanning corresponding direction”. A divergent light beam from a light source 10 which is a semiconductor laser is coupled to an optical system thereafter by a coupling lens 15. The light beam after the coupling may be a parallel light beam, or may be a light beam having a weak divergence or a weak convergence. The coupled light beam then passes through the aperture 20 to remove the light beam peripheral portion by shielding the light beam, thereby performing so-called “beam shaping”. The beam shaped beam passes through the cylinder lens 25 having a positive power only in the sub-scanning corresponding direction (in the plane of FIG. 1A, a direction orthogonal to the principal ray of the beam from the light source 10). Lens 25
The light is condensed in the sub-scanning corresponding direction by the action and enters the deflecting / reflecting surface 31 of the optical deflector 30 which is a rotating polygon mirror while being converged in the sub-scanning corresponding direction. (A direction perpendicular to the drawing) is formed as a long line image. The light beam reflected by the deflecting / reflecting surface 31 enters the scanning and imaging optical system 41 and is condensed as a light spot on the surface to be scanned 50 by the action of the scanning and imaging optical system 41. The reflected light beam is deflected at a constant angular velocity as the light deflector 30 rotates at a constant speed, and the light spot is scanned on the surface to be scanned 50 (substantially, the photosensitive surface of the photoconductive photosensitive member disposed at this position). Is optically scanned.

In FIG. 1A, the principal ray of the light beam from the light source 10 and the rotation axis 3 of the deflecting / reflecting surface 31 of the light deflector 30 are shown.
0Ax (the rotation axis of the rotary polygon mirror 30 itself) is on the same plane. FIG. 1B is a diagram showing the optical arrangement from the optical deflector 30 to the surface to be scanned in FIG. 1A as viewed from the direction of the rotation axis 30Ax of the deflecting / reflecting surface 31 of the optical deflector 30.
As described above, the principal ray of the light beam from the light source 10 and the rotation axis 30Ax (the rotation axis of the rotary polygon mirror 30 itself) of the deflecting / reflecting surface 31 of the optical deflector 30 are in the same plane.
In (b), this same plane is indicated by a plane PL. As described above, since “the rotation axis 30Ax and the principal ray of the incident light beam from the light source side to the deflecting / reflecting surface 31 are within the plane PL”, the optical scanning is performed symmetrically with respect to the plane PL.

The scanning image forming optical system 41 is configured as a "single lens", and has a function of making light scanning by a light spot at a constant speed, and a position of the deflecting / reflecting surface 31 and the position of the surface 50 to be scanned are sub-scanned. And a function of making them substantially conjugate in geometrical optics in the corresponding direction, and has a correction refraction surface 41B.

In summary, in the embodiment shown in FIG. 1, the light beam from the light source 10 is applied to the deflecting / reflecting surface 31 of the optical deflector 30,
Incident on the rotation axis 30Ax obliquely and is deflected at an equal angular velocity to converge the deflected light beam as a light spot on the surface 50 to be scanned, and to impinge the light beam from the light source 10 on the deflected reflection surface 31 Plane PL including direction and rotation axis 30Ax
The optical deflector 30 is a “rotating polygon mirror”, and the optical deflector 30 is a “rotating polygon mirror”. Rotary axis 3
0Ax is incident from a direction obliquely intersecting, and formed as a long linear image in the main scanning corresponding direction near the deflecting / reflecting surface 30, and is deflected at a uniform angular velocity by the rotating polygon mirror 30 to collect the deflected light flux as a light spot. A plane PL including the direction of incidence of the light beam from the light source 10 and the rotation axis 30Ax
This is an optical scanning device that performs optical scanning symmetrically and at a constant speed with respect to.

Then, the scanning image forming optical system "is made incident on the rotation axis 30Ax of the deflecting reflection surface from a direction obliquely intersecting the light and deflects it at a uniform angular velocity, and condenses the deflected light beam as a light spot on the surface to be scanned. Deflection / reflection surface 3 of light flux from light source 10 side
In the optical scanning device that performs optical scanning symmetrically with respect to a plane including the direction of incidence on the light source 1 and the rotation axis 30Ax, a scanning unit that collects a light beam from the light source 10 on the surface 50 to be scanned as a light spot. The image forming optical system is composed of a single lens 41 (Claims 1 and 2) and has a correction refraction surface 41B for correcting the bending of a scanning line (Claims 1 and 2).
1B is the “lens surface located closest to the surface 50 to be scanned” (claim 3). As described above, the scanning image forming optical system 41 has a function of equalizing the speed of optical scanning by a deflected light beam deflected at a constant angular velocity (claim 4). It has a function of making the position of the surface 50 to be scanned substantially geometrically optically conjugate in the direction corresponding to the sub-scanning.

The correction refraction surface 41B is provided with the above-mentioned incident surface such that the intrinsic inclination β ₄₁ in the sub-scan section at the incident position of the deflected light beam on the correction refraction surface 41B “corrects the scan line bending inherent to the optical scanning device”. It is determined according to the position.

[0030]

EXAMPLES Specific examples will be described below. As the light source 10, a semiconductor laser having an emission wavelength of 780 nm was used.
On the optical path from the light source to the surface to be scanned, the i-th surface counted from the light source (including the lens surface of each lens, the cover glass of the semiconductor laser unit, and the deflecting reflection surface)
, The radius of curvature in the main / sub-scanning corresponding direction (the radius of paraxial curvature in the case of a non-arc shape) is Rmi, Rsi, the surface distance between the i-th surface and the (i + 1) -th surface is Di, and the refraction is The refractive index of the material of the optical member having a surface is represented by N.

I Rmi Rsi Di ZN Optical member 0 4.45 -3.40 1.511 Semiconductor laser 1 ∞ 0.30 Cover glass 2 ∞ 2.00 3 ∞ ∞ 2.50 1.675 Coupling lens 4 -5.3856 -5.3856 14.00 5 ∞ 45.995 3.0 1.519 Cylinder lens 6 ∞ ７ 7 ∞ ∞ 38.21 Deflective reflecting surface 8 199.5 -40.03 18.00 1.519 Scanning optical system 9 -212 -15.85 17.00.

The principal ray of the light beam from the light source side is shown in FIG.
As shown in (2), the light is incident on the plane SF orthogonal to the rotation axis 30Ax of the optical deflector 30 so as to form an angle of “3 degrees”. Therefore, the angle formed by the incident principal ray and the rotation axis 30Ax is 87 degrees.

The action of the coupling lens is a “collimating action”, and the coupled light flux is a “parallel light flux”.
Becomes In addition, Z is the deflection reflecting surface 3 in FIG.
When the deflection angle of the deflected light beam due to 1 is 0, that is, in a state where the principal ray of the deflected light beam is within the plane PL of FIG.
The shift amount (mm) of the “light source light emitting unit” downward from the plane SF orthogonal to the rotation axis 30Ax. Scanning optical system 41
Is specified as follows. That is, the “shape in a plane including the symmetry axis and parallel to the main scanning direction” of the incident side surface is widely related to the aspheric surface when the X axis is taken in the symmetric axis direction and the Y axis is taken in the main scanning direction. The known equation, ie, Rm is the paraxial radius of curvature, K, A, B, C, D,. . .
X (Y) = Y ² / [Rm + Rm√ {1- (1 + K) (Y / R
m) ² }] + A · Y ⁴ + B · Y ⁶ + C · Y ⁸ + D · Y
¹⁰ +. . . And paraxial radius of curvature: Rm and constants: K, A, B,
C, D,. "Non-arc shape" specified by.

At the incident side surface 41A, the above Rm, K,
A, B, C, and D are as follows. Rm = -199.5, K = -35.138, A = -1.
98E-7, B = 2.17E-7, C = 1.9E-1
5, D = -1.88E-19.

The curvature Cs in the “sub-scan section” of the incident side surface 41 A of the scanning image forming optical system 41 is Cs (Y) = ｛1 / Rs (0) according to the coordinate Y in the main scanning corresponding direction. It changes according to the equation represented by｝ + 変 化 a _j · Y ** 2j. j is a natural number: 1,
2, 3,. . . It is. “Y ** 2j” is “Y 2j
To the power.

For the incident side surface 41A, the above Rs (0),
a _j is as follows.

Rs (0) =-40.03, a ₁ = 7.31
_{E-6, a 2 = -1.15E} -8, a 3 = 1.3E-1
_{1, a 4 = -8.28E-15} , a 5 = 2.9E-1
_{8, a 6 = -5.07E-22} , a 7 = 3.36E-2
6 As described above, the shape of the incident side surface 41A is specified.

The shape of the exit side surface 41B of the scanning image forming optical system 41 is specified as follows. The emission side surface 41B is a “correction refraction surface” as described above, and has a specific inclination: β in the sub-scan section.
₄₁ is determined according to the incident position such that “scanning line bending inherent to the optical scanning device is corrected”. In other words, the intrinsic inclination: β ₄₁ is a function of the coordinate in the main scanning corresponding direction: Y: β
₄₁ (Y).

In order to specify the shape of the emission side surface 41B, first, the case where the intrinsic inclination is β ₄₁ (Y) ≡0 is considered as a “design criterion”, and the design criterion includes the axis of symmetry of the emission side surface 41B. The shape in the plane parallel to the scanning corresponding direction and the shape in the sub-scanning cross section are given using the above formula: X (Y) and curvature: Cs (Y), as in the case of the incident side surface 41A. Shape is specified by giving intrinsic slope: β ₄₁ .

The above-mentioned Rm, K, A, B, C, and D in the design standard for the emission side surface 41B are as follows. Rm = −212, K = 2.106, A = −3.71E
-7, B = 1.71E-11, C = -5.93E-1
5, D = 1.49E-18.

For the emission side surface 41B, the above Rs (0), a _j in the design standard are as follows. Rs (0) = - 15.85, a 1 = 3.19E-6, a 2
_{= -9.13E-10, a 3 =} -5.37E-12, a 4
_{= 6.49E-15, a 5 =} -3.42E-18, a 6 =
In the _{8.49E-22, a 7 = -8.07E} -26 above, the shape of the "design criteria" of the incident side surface 41A is identified.

Before specifying the "inherent inclination", a supplementary explanation will be given. In the above data, “E and the numerical value following it” represent “power of 10”. For example, “E-9” means “10 to ⁹ ”, and this numerical value is applied to the immediately preceding numerical value. When the optical arrangement shown in FIG. 1 is realized according to the data, when the scanning image forming optical system 41 is in the state of the design standard (the state of the intrinsic inclination: β ₄₁ (Y) ≡0), “bending of the scanning line” occurs. I do. The scanning line bending that occurs in this way is
It is due to the optical arrangement and results from the optical design. Accordingly, the “scanning line bending” existing in this state is the “scanning line bending inherent to the optical scanning device”, and this is shown by a curve 2-2 in FIG.

The intrinsic slope: β ₄₁ (Y) can be “given a functional form as an analytical expression” as a function of the coordinate: Y. Here, the discrete values for some typical Y coordinate values are Give as a list.

Intrinsic slope: β ₄₁ (Y); Y (mm) β ₄₁ (Y) (degrees) -60 0.25505 -45 0.15855 -30 0.11746 -15 0.04090 0 0.00000 15 0.04090 30 0.11746 45 0.15855 60 0.25505

The characteristic inclination β ₄₁ (Y) over the entire Y coordinate range can be obtained by smoothly complementing the above “skip value”.

When the intrinsic inclination: β ₄₁ (Y) is given as described above, the “curvature center line (design basis) in which the center of curvature in the sub-scan section of the emission side surface 41 B, ie, the“ correction refraction surface ”, continues in the main scanning direction. In the state, it is in a plane that includes the axis of symmetry and is parallel to the main scanning corresponding direction).

By inserting a correction refraction surface having the above-mentioned specific inclination, the scanning line curve is corrected as shown by a curve 2-1 in FIG. 2, and the scanning line curve is substantially completely corrected, and is extremely straight. Good optical scanning can be realized. The “table” in FIG. 2 is a numerical value of the scanning line bending.

The scanning imaging lens as in the embodiment is
A mold corresponding to each lens surface is produced by a three-dimensional surface shape forming apparatus, and plastic molding using this mold allows easy and large-volume production, and therefore, inexpensive production.

[0049]

As described above, according to the present invention, a novel scanning image forming optical system and optical scanning device can be realized. The scanning image forming optical system according to the present invention can satisfactorily correct the "scanning line bending inherent in the optical scanning device" due to the non-planar surface on which the deflecting light beam is swept by the correction refraction surface, and can perform main scanning. It is possible to realize a very good optical scanning by linearization. According to the second aspect of the present invention, since the scanning imaging lens is a single lens, the manufacturing cost is low and the optical scanning device can be easily made compact. further,
The scanning image forming optical system according to the third aspect of the present invention is easy to design, and the scanning image forming optical system according to the fourth aspect of the present invention can easily realize the uniform speed of optical scanning. By using this scanning imaging system, the tilting of the deflecting reflection surface of the rotary polygon mirror can be effectively corrected.

Since the optical scanning device of the present invention uses the above-described scanning image forming optical system, the optical system portion from the light source to the optical deflector and the optical system after the optical deflector can be arranged so as to be vertically overlapped. The floor area can be made small and compact. Further, since optical scanning is performed symmetrically with respect to a plane including the direction of incidence from the light source side to the deflecting reflection surface and the rotation axis, even if sag occurs, it occurs symmetrically at an image height of 0. Therefore, it is easy to correct the constant velocity characteristic and the curvature of field in the scanning image forming optical system.

[Brief description of the drawings]

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

FIG. 2 is a diagram for explaining a scanning line bending correction effect in the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Light source 30 Optical deflector 31 Deflection / reflection surface 30Ax Rotation axis of deflection / reflection surface 41 Scanning optical system 41A Incident side surface 41B Exit side surface (corrected refraction surface) 50 Scanned surface

Claims (7)

[Claims] 1. A light beam from a light source is incident on a deflecting / reflecting surface of an optical deflector from a direction obliquely intersecting with a rotation axis of the deflecting / reflecting surface, and is deflected at a uniform angular velocity. A light spot from the light source side, and symmetrically scans light with respect to a plane including the direction of incidence of the light flux from the light source side on the deflection / reflection surface and the rotation axis. A scanning image forming optical system for converging light as a light spot on a surface to be scanned, comprising at least one lens, wherein at least one surface of the lens has a correction refraction for correcting a bending of a scanning line. The correction refraction surface has a tilt at the incident position so that the inherent inclination in the sub-scan section at the incident position of the deflected light beam on the correction refraction surface corrects the scan line bending unique to the optical scanning device. It is characterized by being determined according to査結 image-forming optical system. 2. A scanning image forming optical system according to claim 1, wherein said scanning image forming system comprises a single lens and is arranged on an optical path between said optical deflector and a surface to be scanned. Optical system. 3. The scanning image forming optical system according to claim 1, wherein the lens surface closest to the surface to be scanned is a correction refractive surface. 4. A scanning image forming optical system according to claim 1, wherein said scanning image forming optical system has a function of equalizing the speed of light scanning by a deflected light beam deflected at a constant angular velocity. . 5. A scanning image forming optical system according to claim 1, wherein the vicinity of the starting point of deflection by the optical deflector and the position of the surface to be scanned are geometrically optically conjugated in the sub-scanning corresponding direction. A scanning image forming optical system having a function of making a relationship. 6. A light beam from a light source is incident on a deflecting / reflecting surface of an optical deflector from a direction obliquely intersecting with a rotation axis of the deflecting / reflecting surface, and is deflected at a uniform angular velocity. 2. An optical scanning device which condenses light as a light spot, and performs optical scanning symmetrically with respect to a plane including the direction of incidence of the light beam from the light source side on the deflecting / reflecting surface and the rotation axis, An optical scanning apparatus using the scanning image forming optical system according to any one of the above-described items 1 to 4. 7. A luminous flux from a light source is incident on a deflecting and reflecting surface of a rotating polygonal mirror which is an optical deflector from a direction obliquely intersecting with a rotation axis of the rotating polygonal mirror, and a main scanning corresponding to the vicinity of the deflecting reflecting surface. In addition to forming an image as a long linear image in the direction, the light is deflected at a constant angular velocity by the rotating polygon mirror, the deflected light beam is condensed as a light spot on the surface to be scanned, and the incident direction of the light beam from the light source side and the rotation An optical scanning device that performs optical scanning symmetrically with respect to a plane including an axis, wherein the optical scanning device uses the scanning image forming optical system according to claim 5.