JPH08248341A - Light scan optical system - Google Patents

Abstract

PURPOSE: To excellently correct image and fθ characteristics in the main scan direction and image curvature in the sub-scan direction by single convex lens by constituting the surface on the surface side to be scanned of the convex lens so that a sectional shape formed by a plane parallel to a central optical axis and orthogonally crossed to the main scan direction is nearly fixed in the longitudinal direction. CONSTITUTION: This system is constituted so that luminous flux reflected on a deflecting reflection surface 1a of a rotary polygon mirror 1 constituting an optical deflector is image-formed and scanned on the surface 3a to be scanned of a photoreceptor drum 3. Then, the surface on the surface to be scanned side of the convex lens 2, that is, a light emitting surface is formed into an anamorphic surface. The anamorphic surface is constituted so that the sectional shape D2 formed by the plane D1 parallel to the central optical axis 2a and orthogonally crossed to the main scan direction is nearly fixed in the longitudinal direction, or is the same radius of curvature. Thus, the image and the fθ characteristics in the main scan direction and the image curvature in the sub-scan direction are corrected simultaneously.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention deflects a light beam from a laser light source by an optical deflector having a deflecting / reflecting surface and collects the deflected light beam as a light spot on a surface to be scanned by an optical scanning optical system. The present invention relates to an optical scanning optical system that performs optical scanning.

[0002]

2. Description of the Related Art A light beam from a laser light source is deflected at a constant angular velocity by an "optical deflector having a deflecting / reflecting surface" such as a rotating polygon mirror, a rotating single-sided mirror, or a rotating two-sided mirror, and the deflected light beam is optically scanned. 2. Description of the Related Art Optical scanning devices that perform optical scanning by condensing light spots on a surface to be scanned by a system are widely known in optical printers, digital copying machines, and the like.

In this optical scanning device, in the rotating polygonal mirror, the "variation" of the parallelism of the plurality of deflecting / reflecting surfaces with respect to the rotation axis, and also in the rotating single-sided mirror or the rotating two-sided mirror, the "blur" of the rotation axis causes There is a problem of so-called “face-up” in which the scanning line position of the light spot fluctuates in the sub-scanning direction.

As an effective method of correcting this surface tilt, a light beam from a light source is conventionally formed as a line image in the main scanning direction at a position near the deflecting reflection surface in the sub-scanning direction. A function of making the position of the deflecting / reflecting surface and the position to be scanned have a geometrical-optical conjugate relationship with respect to the sub-scanning direction is provided. The optical scanning optical system of such an optical scanning device is an “anamorphic” imaging optical system in which the power in the main scanning direction and the power in the sub scanning direction are different.

[0005]

By the way, in order to realize good optical scanning by the optical scanning device, "the diameter of the optical spot does not largely change depending on the image height" and "the moving speed of the optical spot is constant. "It is necessary. Of these, the "variation of the light spot diameter depending on the image height" occurs due to the field curvature of the optical scanning optical system, but if the light spot diameter varies depending on the image height, the resolution of the image written by the optical scanning becomes uniform. I won't. Regarding the main scanning direction, even if there is some variation in the light spot diameter, it is possible to correct it by electrically controlling the signal to be placed on the deflected light beam, but the light spot diameter variation in the sub-scanning direction can be corrected in this way. I can't. As for the "uniform velocity of the moving speed of the light spot", the fθ characteristic of the optical scanning optical system and the field curvature in the sub-scanning direction must be well corrected. However, in an anamorphic lens, it is not easy to satisfactorily correct the fθ characteristic and the field curvature in the sub scanning direction at the same time, and a plurality of lenses are combined to form an optical scanning optical system.

For example, when the fθ characteristic is corrected by a convex lens and the aberration in the main scanning direction (the image plane in the main scanning direction and the fθ characteristic) is satisfied, the surface (rear surface) on the scanned surface side of the convex lens is deflected. The curvature becomes larger than that of the surface on the reflection surface side (front surface). At this time, if it is attempted to satisfy the scanning optical system with a single lens, the surface on the surface to be scanned (rear surface) is a toric surface and the deflection reflection surface and the surface to be scanned. Must be conjugated,
The sub-scanning image plane tends to be undercorrected. An example of the field curvature characteristic and the fθ characteristic due to this toric surface is shown in FIG.
(A) and (b). The broken line in FIG. 5A represents the image plane in the main scanning direction, and the solid line in the drawing represents the image plane in the sub scanning direction.

As described above, conventionally, it is difficult to obtain good image plane and fθ characteristics in the main scanning direction and field curvature correction in the sub scanning direction at the same time with a single convex lens. No. 210815, a f.theta. Lens composed of a convex lens is separately combined with a correction lens for correcting the image plane, which complicates the overall structure and lowers productivity.

Therefore, according to the present invention, the image plane in the main scanning direction and f
An object of the present invention is to provide an optical scanning optical system in which the θ characteristic and the correction of the field curvature in the sub-scanning direction can be satisfactorily obtained with one convex lens.

[0009]

To achieve the above object, the present invention has a function of fθ in the main scanning direction, and the deflection reflection surface position and the scan surface position are substantially conjugate in the sub-scanning direction in terms of geometrical optics. With such a relationship, in the optical scanning optical system having the correction function of correcting the surface tilt in the sub-scanning direction, one surface of the surface to be scanned is convex in both the main scanning direction and the sub-scanning direction. The convex lens has a surface configuration in which the side surface to be scanned of the convex lens has a plane shape in which a cross section of a plane parallel to the central optical axis and orthogonal to the main scanning direction is substantially constant in the longitudinal direction.

In the present invention, for example, as shown in FIG. 1A, the light beam reflected by the deflection reflection surface 1a of the rotary polygon mirror 1 constituting the optical deflector is optically scanned according to the present invention. An image is formed and scanned on the surface to be scanned 3a of the photosensitive drum 3 through the convex lens 2 forming the optical system, and the surface of the convex lens 2 forming the optical scanning optical system on the surface to be scanned side. That is, the light emitting surface is formed on the anamorphic surface as described above. As shown in FIG. 1B, the anamorphic surface has a sectional shape D formed by a plane D1 which is parallel to the central optical axis 2a and orthogonal to the main scanning direction.
2 has a surface configuration that is substantially constant or has the same radius of curvature in the longitudinal direction, and by this surface configuration, the image surface and fθ characteristics in the main scanning direction and the correction of the image surface curvature in the sub-scanning direction are simultaneously obtained. Has become. A lens 4 for adjusting the magnification in the sub-scanning direction is arranged on the deflection surface side of the convex lens 2, that is, on the rotary polygon mirror 1 side. The lens 4 for adjusting the magnification in the sub-scanning direction is a lens for adjusting the magnification in the sub-scanning direction when the magnification in the main scanning direction of the convex lens 2 is changed, and therefore is not necessarily provided.

As described above, according to the present invention, the cross-sectional shape of a plane having positive power in both the main scanning direction and the sub-scanning direction, parallel to the central optical axis, and orthogonal to the main scanning direction is substantially in the longitudinal direction. By the one convex lens 2 having a constant anamorphic surface on the surface to be scanned, the image surface in the main scanning direction and the fθ characteristic are excellently obtained, and at the same time, the curvature of field in the sub scanning direction is well corrected. .

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below. Each of the embodiments described below has as its premise
After the light flux from the laser light source is collimated, it is converged only in the sub-scanning direction, and is imaged as a "long line image in the main scanning direction" in the vicinity of the deflective reflection surface of the optical deflector. Then, the light is deflected at a constant angular velocity by the light deflector and is condensed as a light spot on the surface to be scanned through the light scanning optical system.

Therefore, in the optical scanning optical system according to the present invention, the "infinity on the light source side and the position of the surface to be scanned" are brought into a focused positional relationship, that is, a conjugate relationship with respect to the main scanning direction, and in the sub scanning direction. The "position of the deflecting / reflecting surface and the position of the surface to be scanned" are in a conjugate relationship.

The optical scanning optical system in the first embodiment of the present invention shown in FIG. 3 comprises one convex lens 21 having the anamorphic surface described above. The deflecting reflection surface of the optical deflector (not shown) is represented by reference numeral "1", the surface (front surface) of the convex lens 21 according to the present invention on the side of the deflecting reflection surface is represented by reference numeral "2", and the convex lens 21 is scanned. The surface (rear surface) on the surface side is represented by reference numeral "3". At this time, the radius of curvature ri of the lens surface in the main scanning direction (hereinafter,
The line i corresponds to the sign of each surface), the radius of curvature r'i in the sub-scanning direction, the distance di on the (i + 1) th optical axis from the i-th surface, and the refractive index ni for the wavelength 780 nm of the laser light source. Are configured with the following values, respectively.

I r r'i di n i 1 0.0000 0.0000 32.6000 1.00000 2 183.4000 183.4000 16.9500 1.48601 3 -64.1300 -15.4000 97.0000 1.00000

Here, the first surface is a deflecting / reflecting surface of the optical deflector, which is a plane, but is represented as r1 = 0.0000 for convenience. Next, the second surface is x = (1 / r) y ² / {1 + √ [1- (1 + k) y ² /
r ² ]} + ay ⁴ + by ⁶ + cy ⁸ + dy ¹⁰ is configured as a rotating aspherical surface x, and the aspherical coefficient in the above equation is k = 0.0000E + 00 a = -0.89700E-06 b = 0.27800. E-09 c = 0.0000E + 00 d = -0.24600E-16 However, r = r2 = r'2 a = -0.89700E-06 represents -0.89700 × 10 ^-6 (the same applies below). (Note that the radius of curvature at the optical axis is r2 = r'2
= 183.4000).

The focal length FL is FL = 100.003. Next, the third surface is the surface (rear surface) on the surface to be scanned of the convex lens 21, and is represented by both r3 = -64.1300 and r'3 = -15.4000 in both the main scanning direction and the sub scanning direction. When a cross section of a plane having positive power (focusing property) and parallel to the central optical axis and orthogonal to the main scanning direction is seen, the cross-sectional shape is the longitudinal direction, that is, at which point in the main scanning direction. Even if seen, it has a constant surface shape with the same radius of curvature.

As shown in FIG. 2, the center of rotation of the optical deflector 1 is O, the radius of the inscribed circle of the optical deflector 1 is Pr, the deflective reflection surface 1a of the optical deflector 1 and the optical scanning optical system. Convex lens 2
Of the incident optical axis 2b with respect to the deflective reflecting surface 1a of the optical deflector 1 is A, and its incident point A
Where θ is the angle formed by the incident optical axis 2b with the optical axis 2a, and Px and Py are the distances from the incident point A to the rotation center O of the optical deflector 1 in the optical axis direction and the optical axis orthogonal direction. In the first embodiment, Pr = 13.2 θ = 80 ° Px = 10.17 Py = 8.82.

The field curvature characteristic and the fθ characteristic according to the first embodiment are shown in FIGS. 4 (a) and 4 (b). Of these, the broken line in FIG. 4A represents the image plane in the main scanning direction,
The solid line in the figure represents the image plane in the sub-scanning direction.

Next, the optical scanning optical system according to the second embodiment of the present invention shown in FIG. 6 also comprises one convex lens 22 having the anamorphic surface described above.
On the deflection surface side of the convex lens 22, that is, on the rotary polygon mirror side, a magnification adjusting lens 2 for matching the image surface in the sub-scanning direction with the image surface in the main scanning direction when the magnification in the sub-scanning direction is lowered.
3 are arranged.

The deflecting reflecting surface of the optical deflector (not shown) is represented by reference numeral "1", and the deflecting reflecting surface side (front surface) and the surface to be scanned side (rear surface) of the magnification adjusting lens 23 are indicated by reference numeral "1". 2 and 3 respectively, and the surfaces of the convex lens 22 according to the present invention on the side of the deflective reflection surface (front surface) and the surface on the side of the scanned surface (rear surface) are represented by reference numerals “4” and “5”, respectively. , Radiuses of curvature ri, r'in the main and sub directions of the lens surface
Distance di on the (i + 1) th optical axis from the i, i-th surface
, The refractive index ni with respect to the wavelength of 780 nm is constituted by the following values.

I r r'i di n i 1 0.0000 0.0000 16.9000 1.00000 2 0.0000 0.0000 2.0000 1.48601 3 0.0000 6.8000 13.5000 1.00000 4 127.4000 127.4000 16.9000 1.48601 5 -75.1700 -12.3800 95.7000 1.00000

The fourth surface is composed of the same aspherical surface x as in the first embodiment, and the aspherical surface coefficient is k = 0.0000E + 00 a = -0.10728E-05 b = 0.35661E-09 c = 0.0000E. It is +00 d = -0.44641E-16.

The focal length FL is FL = 100.002 and Pr = 13.1 θ = 80 ° Px = 10.112 Py = 8.89.

The fifth surface is the surface (rear surface) on the surface to be scanned of the convex lens 22. As shown by r5 = -75.1700 and r'5 = -12.3800, the fifth surface is in the main scanning direction and the sub-scanning direction. It has a positive power in both directions, and has a surface shape in which a cross section by a plane parallel to the central optical axis and orthogonal to the main scanning direction is constant in the main scanning direction. The field curvature characteristic and the fθ characteristic according to the second embodiment are shown in FIGS. 7A and 7B, respectively. Of these, the broken line in FIG. 7A represents the image plane in the main scanning direction, and the solid line in the figure represents the image plane in the sub scanning direction.

The magnification adjusting lens 23 in the second embodiment is r2 = r'2 = 0.0000, r3 = 0.0000, r'3.
= Cylindrical concave lens represented by 6.8000,
It has a function of matching the image planes in the main scanning direction and the sub scanning direction when the fluctuation in the sub scanning direction is suppressed to be small by shortening the focal length in the sub scanning direction.

Next, the optical scanning optical system in the third embodiment of the present invention shown in FIG. 8 is composed of one convex lens 24 having the anamorphic surface described above.
On the deflection surface side of the convex lens 24, that is, on the rotary polygon mirror side,
A magnification adjusting lens 25 for reducing the magnification in the sub-scanning direction is arranged.

The deflecting reflection surface of the optical deflector (not shown) is represented by reference numeral "1", and the surface on the deflection reflection surface side (front surface) and the surface on the scanned surface side (rear surface) of the magnification adjusting lens 25 are represented by reference numeral "1". 2 "and" 3 "respectively, and the surfaces of the convex lens 24 according to the present invention on the side of the deflective reflection surface (front surface) and the surface on the side of the scanned surface (rear surface) are represented by reference numerals" 4 "and" 5 ", respectively. , Radiuses of curvature ri, r'in the main and sub directions of the lens surface
Distance di on the (i + 1) th optical axis from the i, i-th surface
, The refractive index ni with respect to the wavelength of 780 nm is constituted by the following values.

I r i r'i di n i 1 0.0000 0.0000 14.6000 1.00000 2 -36.4600 -36.4600 2.2000 1.48601 3 -36.4600 7.3000 10.9000 1.00000 4 256.0000 256.0000 16.0000 1.48601 5 -61.8500 -11.0800 99.2000 1.00000

The first surface is a deflecting / reflecting surface of the optical deflector,
The third surface is an anamorphic surface with r3 = -36.4600 and r'3 = 7.3000. Further, the second surface and the fourth surface are composed of a rotational aspherical surface x represented by the following formula, and x = (1 / r) y ² / {1 + √ [1- (1 + k) y ² /
r ² ]} + ay ⁴ + by ⁶ + cy ⁸ + dy ¹⁰ + ey ¹² However, r = r 2 = r ′ 2 or r = r 4 = r ′ 4 The aspherical surface coefficient on the second surface is k = 0.0000E + 00 a = 0.0000E +00 b = 0.12132E-08 c = 0.00000E + 00 d = 0.00000E + 00 e = -0.00000E + 00 The aspherical surface coefficient on the 4th surface is k = 0.00000E + 00 a = -0.777407E-06 b = 0.24264E-09 c = 0.00000E + 00 d = -0.22321E-16 e = 0.00000E + 00.

The focal length FL is FL = 99.99 and Pr = 16.06 θ = 80 ° Px = 12.49 Py = 11.42.

The fifth surface is the surface (rear surface) on the scanned surface side of the convex lens 24, and r5 = -61.8500, r'5 = -11.0800.
The cross-section of a plane that has positive power in both the main scanning direction and the sub-scanning direction and that is parallel to the central optical axis and is orthogonal to the main scanning direction is a surface shape that is constant in the longitudinal direction. There is. The field curvature characteristic and the fθ characteristic according to the third embodiment are shown in FIGS. 9A and 9B, respectively. Of these, the broken line in FIG. 9A represents the image plane in the main scanning direction, and the solid line in the figure represents the image plane in the sub scanning direction.

The magnification adjusting lens 25 in the third embodiment is a toric lens whose surface indicated by reference numeral 3 has a negative power (divergence) in the sub-scanning direction, and the focal length in the sub-scanning direction should be shortened. Has a function of matching the image planes in the main scanning direction and the sub scanning direction when suppressing the fluctuation in the sub scanning direction.

Further, a fourth aspect of the present invention shown in FIG.
The optical scanning optical system in the embodiment is also composed of one convex lens 26 having the anamorphic surface described above. However, a magnification for reducing the magnification in the sub-scanning direction is provided on the deflection surface side of the convex lens 26, that is, on the rotary polygon mirror side. Adjustment lens 27
Is arranged.

The deflecting reflection surface of the optical deflector (not shown) is indicated by reference numeral "1", and the deflection reflection surface side (front surface) and the surface to be scanned side (rear surface) of the magnification adjusting lens 25 are indicated by reference numeral "1". 2 "and" 3 ", respectively, and when the surface of the convex lens 26 according to the present invention on the side of the deflection reflection surface (front surface) and the surface on the side of the surface to be scanned (rear surface) are represented by reference numerals" 4 "and" 5 ", respectively. , Radiuses of curvature ri, r'in the main and sub directions of the lens surface
Distance di on the (i + 1) th optical axis from the i, i-th surface
, The refractive index ni with respect to the wavelength of 780 nm is constituted by the following values.

I r i r'i d i ni 1 0.0000 0.0000 19.0000 1.00000 2 -50.6400 -50.6400 2.2000 1.48601 3 -51.3200 15.8000 3.3000 1.00000 4 280.0000 280.0000 16.0200 1.48601 5 -58.8000 -10.0000 99.5819 1.00000

At this time, the shape x in the main scanning plane of the aspherical surface on the second surface and the anamorphic surface on the third surface
Is x = (1 / r) y ² / {1 + √ [1- (1 + k) y ² /
r ² ]} + ay ⁴ + by ⁶ + cy ⁸ + dy ¹⁰ + ey ¹² and the aspherical surface coefficient on the second surface is k = 0.000E + 00 a = -0.16800E-05 b = 0.60300E-09 c = -0.16600 E-10 d = 0.987000E-13 e = -0.12800E-17 The aspherical surface coefficient on the 3rd surface is k = 0.0000E + 00 a = 0.0000E + 00 b = 0.0000E + 00 c = 0.0000E + 00 d = 0.38000E-13e = 0.00000E + 00.

The focal length FL is FL = 100.07, and Pr = 11.6 θ = 80 ° Px = 8.97 Py = 7.96.

The field curvature characteristics and the fθ characteristics according to the fourth embodiment are shown in FIGS. 11 (a) and 11 (b), respectively. Of these, the broken line in FIG. 11A represents the image plane in the main scanning direction, and the solid line in the figure represents the image plane in the sub scanning direction.

The surface indicated by reference numeral 3 of the magnification adjusting lens 27 in the fourth embodiment has a surface shape in which the cross section by a plane parallel to the central optical axis and orthogonal to the main scanning direction is constant in the longitudinal direction, and the sub scanning is performed. It consists of an anamorphic lens with negative power in the direction, and has a function to match the image plane in the main scanning direction and the image surface in the sub scanning direction when the fluctuation in the sub scanning direction is kept small by shortening the focal length in the sub scanning direction. ing.

Although the invention made by the present inventor has been specifically described based on the embodiments, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention. Needless to say. For example, the optical deflector is not limited to the rotary polygon mirror such as the polygon mirror as in each of the above-described embodiments, but the one deflecting at a constant angular velocity such as a rotary single-sided mirror or a rotary two-sided mirror. If so, the same can be applied.

[0042]

As described above, in the optical scanning optical system according to the present invention, the side surface of the surface to be scanned has a positive power (divergence) in both the main scanning direction and the sub scanning direction, and the central optical axis. The image plane in the main scanning direction and the fθ characteristic and the sub-scanning direction are formed by a single convex lens having an anamorphic surface whose cross-sectional shape in a plane parallel to and parallel to the main scanning direction is substantially constant in the longitudinal direction. Correction of the field curvature of
Since it can be obtained by one convex lens, the structure of the optical scanning optical system can be simplified and the productivity can be improved.

[Brief description of drawings]

FIG. 1 is an explanatory plan view showing a principle configuration of an optical scanning optical system to which the present invention is applied.

FIG. 2 is an explanatory diagram of a principle configuration showing defined portions of the present invention.

FIG. 3 is an explanatory plan view showing an optical scanning optical system according to the first embodiment of the invention.

FIG. 4 is a diagram showing field curvature characteristics (a) and fθ characteristics (b) according to the first embodiment shown in FIG. 3.

FIG. 5: Field curvature characteristic by a toric single lens (a)
FIG. 3 is a diagram showing an example of the fθ characteristic (b).

FIG. 6 is an explanatory plan view showing an optical scanning optical system according to a second embodiment of the present invention.

FIG. 7 is a diagram showing field curvature characteristics (a) and fθ characteristics (b) according to the second embodiment shown in FIG. 6;

FIG. 8 is an explanatory plan view showing an optical scanning optical system according to a third embodiment of the invention.

9 is a diagram showing field curvature characteristics (a) and fθ characteristics (b) according to the third embodiment shown in FIG. 8. FIG.

FIG. 10 is a plan view showing an optical scanning optical system according to a fourth embodiment of the invention.

11 is a diagram showing field curvature characteristics (a) and fθ characteristics (b) according to the third embodiment shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 rotary deflector 1a deflection reflection surface 2 anamorphic convex lens 3 photoconductor drum 3a scanned surface

Claims (5)

[Claims] 1. A surface tilt in the sub-scanning direction is obtained by having an fθ function in the main scanning direction and by making the position of the deflective reflection surface and the scanned surface position substantially geometrically conjugate in the sub-scanning direction. In the optical scanning optical system having a correcting function, the surface on the side to be scanned has one convex lens convex in both the main scanning direction and the sub-scanning direction, and the surface on the surface to be scanned side of the convex lens. However, the optical scanning optical system is characterized in that a cross-sectional shape of a plane parallel to the central optical axis and orthogonal to the main scanning direction has a substantially constant surface shape in the main scanning direction. 2. The optical scanning optical system according to claim 1, wherein a lens for adjusting magnification in the sub-scanning direction having negative power in the sub-scanning direction is arranged on the deflection surface side of the convex lens according to claim 1. An optical scanning optical system characterized in that 3. A light beam from a laser light source is deflected at an equal angular velocity by an optical deflector having a deflecting reflection surface, and the deflected light beam deflected by the optical deflector is spotted on a surface to be scanned by an optical scanning optical system. In the optical scanning optical system for condensing and performing optical scanning, the optical scanning optical system has one convex lens whose surface on the scanned surface side is convex in both the main scanning direction and the sub scanning direction. The surface of the convex lens on the surface to be scanned has a positive power in both the main scanning direction and the sub-scanning direction, and has a cross-sectional shape of a plane parallel to the central optical axis of the convex lens and orthogonal to the main scanning direction. An optical scanning optical system having a substantially constant surface shape in the main scanning direction. 4. The optical scanning optical system according to claim 3,
An optical scanning optical system, wherein a lens for adjusting magnification in the sub-scanning direction is arranged on the deflecting surface side of the convex lens. 5. The optical scanning optical system according to claim 1, wherein the surface of the convex lens on the surface to be scanned has a sectional shape of a plane parallel to the central optical axis of the scanning light and orthogonal to the main scanning direction. An optical scanning optical system having the same radius of curvature in the main scanning direction.