JP2001075032A - Optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an optical scanner by which focusing position deviation in main and sub scanning directions caused in accordance with the change of ambient temperature can be self-corrected in the entire system of an optical system, and a light spot having a small diameter can be formed on a surface to be scanned regardless of temperature change. SOLUTION: As to the optical scanner provided with a light source 1, the optical system 2 coupling a luminous flux from the light source to the successive optical system, an optical deflector 5 reflecting and deflecting the luminous flux from the coupling optical system by a deflecting and reflecting surface 5a, a scanning and image-forming optical system 6 condensing the deflected luminous flux by the optical deflector on a surface 7 to be scanned as the light spot, and a correction optical system 3 self-correcting the focusing position deviation of the light spot on the surface to be scanned caused in accordance with the ambient fluctuation; the system 3 has at least a pair of a resin lens 3a having an anamorphic surface having negative power both in the main scanning direction and in the sub-scanning direction and a glass lens 3b having the anamorphic surface having positive power at least in the sub-scanning direction, and is set between the system 2 and the surface 5a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a writing optical system of an image forming apparatus such as a laser printer, a digital copying machine, and a facsimile, and an optical scanning apparatus applied to a measuring instrument, an inspection apparatus, and the like.

[0002]

2. Description of the Related Art An optical scanning device which deflects a light beam from a light source by an optical deflector, condenses it as a light spot on a surface to be scanned by a scanning optical system, and scans the surface to be scanned has conventionally been a laser printer. And a digital copier, a facsimile, and the like. In such an optical scanning device, use of a resin lens is intended for the purpose of reducing the lens cost or realizing a special lens surface shape.
In particular, a lens (scanning image forming lens) constituting a scanning image forming optical system for forming an image of a deflected light beam on a surface to be scanned is a special lens for the purpose of excellent correction of constant velocity characteristics such as field curvature and linearity. Various surface shapes have been proposed, but a resin lens is suitable for realizing such a special lens surface shape. On the other hand, as is well known, the resin lens has a problem that the curvature and the refractive index of the lens surface change due to a volume change due to a temperature change, and the lens performance, particularly the focal position of the light spot on the surface to be scanned changes. There is. This change in the focal position causes an increase in the spot diameter of the light spot on the surface to be scanned, causing beam thickening and causing a reduction in the resolution of optical scanning.

Therefore, the change in the focal position due to the change in the temperature of the resin lens occurs in the positive lens and the negative lens in opposite directions. It is known that a resin lens having a power opposite to that of a resin scanning image forming lens is provided on an optical path to reach to cancel a change in a focal position due to a temperature change of the scanning image forming lens (Japanese Patent Laid-Open No. H10-163873). 8-160330, JP-A-8-292388). Here, JP-A-8-1
The optical scanning device described in Japanese Patent No. 60330 has a configuration including a light source, an incident optical system, a deflector, a scanning optical system, and a medium to be scanned, and the incident optical system converts a divergent light beam from the light source into a parallel light beam. An optical system (collimating lens); and a second optical system that forms an image of light from the light source through the first optical system in the sub-scanning direction near the deflector. One of the two optical systems includes a resin optical element (lens) having negative power in the sub-scanning direction. Further, the scanning optical device described in Japanese Patent Application Laid-Open No. 8-292388 has a first image forming portion that forms an image near the deflection position of the deflector, has a negative refractive power only in the sub-scanning direction, and uses resin as a material. A negative lens to perform temperature compensation.

[0004]

However, in the optical scanning device described in the above prior art, the resin lens for correction provided between the light source and the optical deflector has a negative lens only in the sub-scanning direction. Since the lens has power and does not have power in the main scanning direction, it was not possible to correct the focal position shift (deviation of the light spot imaging position) in the main scanning direction due to the temperature change of the scanning imaging lens. Further, since the correction lens in the related art has a normal circular arc cross section, there is a problem that the correction lens deteriorates the wavefront aberration and hinders the reduction of the diameter of the light spot.

The present invention has been made in view of the above circumstances, and even when a resin lens is used in an optical system for forming an image of a deflected light beam on a surface to be scanned, the main scanning direction is affected by a change in environmental temperature. Another object of the present invention is to realize an optical scanning device capable of self-correcting a focal position shift in the sub-scanning direction by an entire optical system and forming a small-diameter light spot on a scanned surface regardless of a temperature change. .

[0006]

As a means for solving the above-mentioned problems, an optical scanning device according to the present invention comprises a light source for emitting a light beam, and a light beam from the light source being converted into a parallel light beam, a substantially convergent light beam, or a substantially divergent light beam. A coupling optical system that converts the light into a light beam and couples the light beam to the subsequent optical system; an optical deflector that reflects the light beam from the coupling optical system on a deflecting / reflecting surface to deflect and scan; And a correction optical system for self-correcting the focal position shift of the light spot on the scanned surface due to environmental fluctuations and the like. The correction optical system includes a resin lens having an anamorphic surface having negative power in both the main scanning direction and the sub-scanning direction,
At least one pair of a glass lens having an anamorphic surface having a positive power at least in the sub-scanning direction is provided, and is provided between the coupling optical system and the deflection reflection surface.

In the optical scanning device according to the first aspect,
It is preferable that the correction optical system composed of a resin lens having an anamorphic surface and a glass lens having an anamorphic surface be integrally held by a holding member. In the optical scanning device according to the second aspect, it is preferable that the correction optical system integrated with the holding member has a structure capable of adjusting the movement in the optical axis direction (claim 3). Alternatively, in the optical scanning device according to the second aspect, it is preferable that the correction optical system integrated with the holding member has a structure capable of rotating and adjusting in a direction perpendicular to the optical axis. Further, in the optical scanning device according to the first, second, third or fourth aspect, it is preferable that at least one of the anamorphic surfaces of the correction optical system is configured to be aspherical in both the main and sub-scanning directions. ). Further, in the optical scanning device according to claim 1, the distance between the resin lens having the anamorphic surface and the glass lens having the anamorphic surface is L, and the sub-scanning of the entire correction optical system is performed. When the focal length in the direction is fs, the condition: 0 <L / fs <
It is preferable to satisfy 0.1 (claim 6).

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure, operation and operation of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a view showing an embodiment of the present invention, and is an optical arrangement in which the arrangement of an optical system constituting an optical scanning device is developed on a main scanning plane (a plane parallel to the optical axis and the main scanning direction). FIG. The optical system shown in FIG. 1 includes a light source 1 that emits a light beam, and a coupling optical system 2 that converts the light beam from the light source 1 into a parallel light beam, a substantially convergent light beam, or a substantially divergent light beam, and couples the light beam with the subsequent optical system. A light deflector 5 for reflecting the light beam from the coupling optical system 2 on the deflecting / reflecting surface 5a and deflecting and scanning the light; and a scanning device for condensing the deflected light beam by the light deflector 5 on the surface 7 to be scanned as a light spot. An image optical system 6 and a correction optical system 3 for self-correcting the focal position shift of the light spot on the surface to be scanned due to environmental fluctuations and the like are provided. The correction optical system 3 includes a resin correction lens 3a having an anamorphic surface having negative power in both the main scanning direction and the sub-scanning direction, and a glass correction lens 3b having an anamorphic surface having at least positive power in the sub-scanning direction. And the coupling optical system 2 and the deflecting / reflecting surface 5a.
(Claim 1). Reference numeral 4 denotes a plane mirror for bending the optical path, which is installed as necessary.

Here, a semiconductor laser is used as the light source 1, but a light emitting diode (LED) may be used. The coupling optical system 2 is a coupling lens composed of a single lens or a plurality of lenses. The coupling optical system 2 converts a divergent light beam emitted from the light source 1 into a parallel light beam, a substantially convergent light beam, or a substantially divergent light beam, and thereafter an optical system. (Coupling optical system). The coupling lens 2 may be a glass lens or a resin lens, but is preferably made of a glass lens that is not easily affected by environmental changes such as temperature. Further, the lens surface may have an aspherical shape in order to eliminate spherical aberration. The correction optical system 3 corrects a focal position shift due to environmental fluctuations (temperature and humidity) in both the main scanning direction and the sub-scanning direction (details will be described later), but usually a line image forming optical system. As shown in (a) an optical path diagram developed on a plane in the main scanning direction and (b) an optical path diagram developed on a plane in the sub-scanning direction, the luminous flux from the coupling lens 2 is It converges in the sub-scanning direction (in FIG. 1, the direction orthogonal to the plane of the paper), and forms an image near the deflecting reflection surface 5a of the optical deflector 5 as a long line image in the main scanning direction. The optical deflector 5 is a rotating polygon mirror (polygon mirror) that rotates at a constant speed around the rotation axis 5b of the motor.
Then, the light beam reflected by the deflecting / reflecting surface 5a is deflected at a constant angular speed by rotating the polygon mirror 5 at a constant speed. Incidentally, as the optical deflector, a rotating single-sided mirror, a rotating two-sided mirror, or the like can be suitably used in addition to the polygon mirror. Scanning optical system 6
1 is constituted by two scanning lenses 6a and 6b in the example of FIG. In the apparatus, the light-sensitive surface or the like of the photoconductive photoreceptor becomes a surface to be scanned. The scanning image forming optical system 6 is not limited to a combination of two lenses, but may be constituted by one lens,
It can also be composed of more than one lens. Further, it may be constituted by a combination of one or more lenses and a concave mirror or fθ mirror having an image forming action. Further, when the scanning image forming optical system 6 is composed of two scanning lenses 6a and 6b as shown in FIG. 1, the correction of the curvature of field in the main and sub scanning directions and the uniform velocity characteristics (linearity, fθ characteristics) are performed. For the purpose of improvement, a resin lens having an aspherical lens surface is used for at least one of the scanning lenses.

Next, the correcting optical system 3 which is a feature of the present invention will be described. As shown in FIGS. 1 and 2, the correction optical system 3
Is a resin correction lens 3a having an anamorphic surface having negative power in both the main scanning direction and the sub-scanning direction, and a glass having an anamorphic surface (including a cylinder surface) having at least a positive power in the sub-scanning direction. Of the anamorphic surface in order to satisfactorily correct the imaging position deviation in the main scanning direction and the imaging position deviation in the sub-scanning direction on the scanned surface 7 due to the fluctuation of the environmental temperature. The temperature dependence of the curvature, the coefficient of linear expansion, and the refractive index is optimally determined.

Here, the correction lenses 3a, 3a of the correction optical system 3
The following effects can be obtained by using 3b as an anamorphic surface. In both main scanning and sub-scanning directions, it is possible to correct a focal position shift due to a change in environment (temperature, humidity). The use of the anamorphic surface allows the opposing surface to be a flat surface, which can be used as a mounting reference surface, thereby suppressing the occurrence of eccentricity that degrades optical performance. With the recent development of cutting and polishing techniques, anamorphic surfaces can be processed relatively easily. Therefore, it can be realized without combining cylinder surfaces, spherical surfaces, and the like as in the past.

The present invention also provides a correction optical system 3 for correcting the focal position shift of the scanning image forming optical system 6 (scanning lenses 6a and 6b) due to the fluctuation of the environment (temperature and humidity) before the deflection reflecting surface 5a of the polygon mirror 5. And the field curvature itself is not basically corrected. Therefore, it is desirable that the curvature of field (deviation of defocus in one scan) of the scanning imaging optical system 6 be corrected well in advance. Therefore, in an embodiment to be described later, the scanning lenses 6a and 6b constituting the scanning image forming optical system 6 will be described.
The surface shape is made an anamorphic surface (for example, a toroidal surface or a special toroidal surface) to improve optical performance such as field curvature and constant velocity characteristics (linearity, fθ characteristics) as shown in FIG. The special toroidal surface is a toroidal surface in which the curvature in the sub-scanning section (a virtual section orthogonal to the main scanning direction) changes in the main scanning direction.

Next, in the optical scanning device having the structure shown in FIGS. 1 and 2, a resin correction lens 3 having an anamorphic surface is provided.
a and glass correction lens 3b having an anamorphic surface
The correction optical system 3 is preferably integrally held by a holding member. For example, as shown in FIG. 3, a resin correction lens 3a and a glass correction lens 3b of the correction optical system 3 are integrated by a correction optical system unit 3c. It is configured to be held.
Further, the outer shape of the correction optical system unit 3c is formed in a cylindrical shape, and is mounted on a pedestal 3d having a V-shaped groove so that the correction optical system unit 3c can be moved and adjusted along the groove in the direction of the optical axis O. It can be configured to be rotatable in a direction perpendicular to the direction.

The following advantages are obtained by integrally forming the correction lenses 3a and 3b constituting the correction optical system 3 by a unit 3c as shown in FIG. When there are a plurality of anamorphic surfaces (two in the correction optical system and four in the scanning optical system in the embodiment described later), rotational eccentricity in a plane perpendicular to the optical axis generates a large wavefront aberration, and Causes fatness. Therefore, by holding the resin correction lens 3a and the glass correction lens 3b of the correction optical system 3 integrally with the optical system unit 3c, the wavefront aberration generated in the correction optical system 3 can be suppressed in advance during the assembly adjustment. (Claim 2). By making the integrated correction optical system movable and adjustable in the direction of the optical axis as shown in FIG. 3, when the correction optical system 3 is assembled in the optical system unit 3c, the focus in the main and sub-scanning directions can be improved. The displacement can be adjusted in advance (claim 3). By making the integrated correction optical system rotatable in a direction perpendicular to the optical axis direction as shown in FIG. 3, it is possible to adjust the entire optical system while maintaining the wavefront aberration in the correction optical system. (Claim 4).

In recent years, writing density has been increasing in image forming apparatuses such as laser printers and digital copiers, and high density writing exceeding 1200 dpi (dots / inch) has been realized. In order to cope with such a high density, it is necessary to reduce the spot diameter of the light spot on the surface to be scanned, and for that purpose, it is necessary to increase the NA of the optical system. Since the light flux transmitted through the optical system increases due to the increase in the NA, the wavefront aberration generated at that time greatly affects the light spot diameter. If the wavefront aberration is too large, it is impossible to narrow down the light spot to a small diameter light spot. Therefore, in the present invention, at least one of the anamorphic surfaces of the two correction lenses constituting the correction optical system 3 is configured to be aspherical in both the main and sub-scanning directions.
More specifically, the correction lens 3 constituting the correction optical system 3
By providing at least one special toroidal surface having a non-circular arc in the main scanning direction or the sub-scanning direction, it is possible to satisfactorily correct wavefront aberration (claim 5). Although a specific embodiment of the correction optical system will be described later, in the embodiment, the concave anamorphic surface on the light incident side (coupling lens side) of the resin lens 3a of the correction optical system is formed as a special toroidal surface. Wavefront aberration is well corrected. FIG. 5 shows (a) a case where a normal circular toroidal surface is used for the concave anamorphic surface on the light incident side of the resin correction lens 3a of the correction optical system 3;
(B) The wavefront aberration when a special toroidal surface is used is shown, and it can be seen that the wavefront aberration is favorably corrected by using the special toroidal surface.

Here, the correction lens 3 of the correction optical system 3
a, 3b and scanning lenses 6a, 6b of the scanning image forming optical system 6.
An expression for specifying the lens surface shape of the special toroidal surface applied to the above will be described. However, the present invention is not limited to this expression. In expressing the lens surface, the coordinates in the main scanning direction near the lens surface are Y, the coordinates in the sub-scanning direction are Z, and their origins are taken as the optical axis. The general formula of the lens surface is f (Y, Z) = fm (Y) + fs (Y, Z). Here, the surface shape of the special toroidal surface in the main scanning cross section (a virtual cross section including the lens optical axis and parallel to the main scanning direction) is a non-arc shape, and the first term on the right side of the above expression fm (Y) represents a shape in the main scanning section, and fs (Y, Z) of the second term is a sub-scanning section at a position of coordinate Y in the main scanning direction (a virtual section orthogonal to the main scanning direction). )
Represents the shape inside.

In the following, the shape in the main scanning section is fm
As (Y), a well-known non-arc-shaped equation, that is, the paraxial radius of curvature in the main scanning section in the optical axis is Rm, the distance from the optical axis in the main scanning direction is Y, the conical constant is Km, Coefficient Am
When Am2, Am3, Am4, Am5,..., The depth in the optical axis direction is represented by X, and is represented by the following polynomial. X = f (Y, Z) = fm (Y) + fs (Y, Z) (1) fm (Y) = (Y ^ 2 / Rm) / [1 + √ {1- (1 + Km) (Y / Rm) ^ 2}] + Am1 Y + Am2 Y2 + Am3 Y3 + Am4 Y4 + Am5 Y5 + In the equation (2), the odd-order coefficient : When any of Am1, Am3, Am5,... Is not 0, the non-circular shape becomes an asymmetric shape in the main scanning direction. Further, even-order coefficients: Am2, Am4, Am6,.
In the case where there is only one, it is symmetric in the main scanning direction. In the above description, for example, "Y ^ 2" represents "Y ² ", and "Y ^ 3" represents "Y ³ ". Further, the above fs (Y, Z) is represented as follows. fs (Y, Z) = (Z ^ 2 ・ Cs) / [1 + √ {1- (1 + Ks) (Z ・ Cs) ^ 2}] + (F0 + F1 ・ Y + F2 ・ Y2 + F3 ・ Y ^ 3 + F4 ・ Y ^ 4 + ・ ・) ・ Z + (G0 + G1 ・ Y + G2 ・ Y ^ 2 + G3 ・ Y ^ 3 + G4 ・ Y ^ 4 + ・ ・) ・ Z ^ 2 + (H0 + H1 Y + H2 Y2 + H3 Y3 + H4 Y4 + ...) Z3 + (I0 + I1Y + I2Y2 + I3Y ^ 3 + I4 ・ Y ^ 4 + ・ ・) ・ Z ^ 4 + (J0 + J1 ・ Y + J2 ・ Y ^ 2 + J3 ・ Y ^ 3 + J4 ・ Y ^ 4 + ・ ・) ・ Z ^ 5 + (K0 + K1 ・ Y + K2 ・ Y ^ 2 + K3 ・ Y ^ 3 + K4 ・ Y ^ 4 + ・ ・) ・ Z ^ 6 + ・ ・ (3) where Cs = (1 / Rs0) + B1・ Y + B2 ・ Y ^ 2 + B3 ・ Y ^ 3 + B4 ・ Y ^ 4 + B5 ・ Y ^ 5 + ・ ・ (4) Ks = Ks0 + C1 ・ Y + C2 ・ Y ^ 2 + C3 ・ Y ^ 3 + C4.Y ^ 4 + C5.Y ^ 5 +... (5), and "Rs0" is a paraxial radius of curvature in the sub-scan section including the optical axis. Also, odd-order coefficients B1, B of Y
When any of 3, B5,... Is not 0, the curvature in the sub-scan section becomes asymmetric in the main scanning direction. Similarly, the coefficient: C
1, C3, C5, ..., F1, F3, F5, ..., G1, G3, G
When any of the odd-order coefficients of Y representing the non-arc amount, such as 5,..., Is other than 0, the non-arc amount in the sub-scan becomes asymmetric in the main scanning direction. In the embodiment described later, the incident surface side of the correction lens (resin lens) 3a on the light source side of the correction optical system 3 is a special toroidal surface expressed by the above equation. The four lens surfaces of the scanning lenses 6a and 6b are special toroidal surfaces represented by the above equations.

Next, in the present invention, in the optical scanning device having the structure shown in FIGS. 1 to 3, a resin lens 3a having an anamorphic surface and a glass lens 3b having an anamorphic surface are provided.
Where L is the surface distance of the correction optical system 3 and fs is the focal length of the entire correction optical system 3 in the sub-scanning direction, the following condition is satisfied: 0.005 <L / fs <0.1 ( Claim 6). Here, if the upper limit of 0.1 of the above condition is exceeded, the distance between the deflecting / reflecting surface 5a of the optical deflector 5 and the correction optical system 3 becomes too long in order to correct the defocus due to environmental fluctuation. Subject to layout restrictions. On the other hand, if the lower limit of 0.005 is exceeded, the negative power of the resin lens 3a becomes too large, so that the wavefront aberration is deteriorated and it becomes difficult to obtain a small-diameter light spot on the surface 7 to be scanned. In the optical system shown in the examples described later, L / fs = 1.0 / 131 = 0.0076.

Now, in the optical scanning device according to the present invention having the above-described configuration, there are a case where temperature correction is performed by the correction optical system 3 (temperature cancellation method) and a case where temperature correction is not performed (no temperature cancellation). Table 1 below shows the result of comparing the image plane fluctuation amount (imaging position shift) in the main and sub-scanning directions with the image plane fluctuation width.

[0020]

[Table 1]

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A specific embodiment of the optical system in the optical scanning device having the structure shown in FIGS. In this embodiment, the light source 1 is a semiconductor laser, and has an emission wavelength of 655.
nm. The coupling lens 2 is a single lens glass lens (FD) held by an aluminum cell member.
10), the focal length is f = 22.0 mm, and the emitted light is a parallel light beam. In the present embodiment, the lens surface on the exit side of the coupling lens 2 is surface number 0, the entrance surface side of the resin correction lens 3a of the correction optical system 3 is surface number 1, and the exit surface side is surface number 2. The incident surface side of the glass correction lens 3b is surface number 3, and the outgoing surface side is surface number 4. The surface number of the deflecting / reflecting surface 5a is 5, and the two scanning lenses 6a and 6b constituting the scanning imaging optical system 6 are 6, 7, 8, and 9 in order from the incident surface side.

The deflecting / reflecting surface 5a of the polygon mirror constituting the optical deflector 5 is a plane and has a natural light condensing point: ∞. This polygon mirror has six deflecting / reflecting surfaces and an inscribed circle radius of 25.
mm, and the rotation center axis 5b and the reflection point (the point of intersection between the light beam and the deflecting reflection surface when the principal ray of the deflecting light beam is parallel to the optical axis of the scanning lenses 6a and 6b) The distance in the optical axis direction is 10.7 mm, and the distance in the main scanning direction is 22.69 mm. When the principal ray of the deflected light beam is parallel to the optical axes of the scanning lenses 6a and 6b, the angle formed by the principal ray and the principal ray of the light beam incident on the deflecting reflection surface from the light source side (that is, a polygon mirror) Incident angle) is 60 degrees. The angle of view is -38 degrees to +3.
8 degrees.

The correction optical system 3 has a focal length: f = 131 mm
The resin-made correction lens 3a has a refractive index: n = 1.
52716, where the first surface is a special toroidal surface having a concave shape and the second surface is a flat surface. The glass correction lens 3b has a refractive index: n = 1.543332 (BK
7) is a toroidal surface in which the third surface is convex in the surface number;
The fourth surface is a plane. The scanning lens 6a on the polygon mirror 5 side of the scanning imaging optical system 6 is made of resin and has a refractive index: n = 1.
52716, and the sixth surface is a special toroidal surface having a concave shape in the surface number, and the seventh surface is a special toroidal surface having a convex shape in which the curvature of the sub-scanning section is asymmetric. The scanning lens 6b on the scanning surface 7 side is made of resin and has a refractive index of n = 1.52716, and the eighth surface has a concave toroidal special toroidal surface having an asymmetric sub-scanning section curvature. Nine surfaces are special toroidal surfaces having a convex shape that is non-circular in both the main and sub-scan sections. Here, lens data of the optical system with respect to the above-described paraxial curvature radii: Rm, Rs0, and the surface interval on the optical axis: x are shown below.

Surface number Rm Rs0 x Correction lens 3a 1 -100.9 -17.76 3.0 2 ∞ ∞ 1.0 Correction lens 3b 3 100.0 15.0 3.0 4 ∞ ∞ 140.64 Deflection / reflection surface 5a 5 ∞ ∞ 72.560 Scanning lens 6a 6 -242.186 242.337 31.572 7- 83.064 138.908 81.808 Scanning lens 6b 8 -239.054 -78.986 9.854 9 -218.790 -26.516 145.001

The first lens 3a of the resin correction lens 3a
The above-described formula for specifying the lens surfaces of the special toroidal surfaces of the surfaces and the sixth to ninth surfaces of the scanning lenses 6a and 6b.
The values of the coefficients in (1) to (5) are shown below. In addition, in each coefficient data shown below, the E added to the end of the numerical value and the numerical value following the numerical value represent that a power of 10 is multiplied. For example, “E-15” means “× 10 ⁻¹⁵ ” are doing.

The first surface: Am1, Am2, Am3, Am4, Am5,... = 0 B2 = −2.9712E-05, B4 = −8.5101E-07, B6 = 4.1938E-09 C0 = 1.8861E + 00, C1 = 4.5792E-02, C3 = -5.6507E-04 I0 = -3.0182E-05, I1 = -9.6650E-07, I3 = 1.2955E-08 K0 = -1.4683E-06, K1 = 4.9604E-08 , K3 = 1.2755E-08

Surface 6: Am2 = 6.9335E-01, Am4 = -3.7002E-09, Am6 = 5.3962E-12 Am8 = -2.6877E-14, Am10 = 3.2892E-18 B2 = -1.0850E-05, B4 = 4.4623E-09, B6 = -1.4980E-12 B8 = -1.1955E-15, B10 = 1.4318E-18, B12 = -3.5225E-22 B14 = -2.8072E-25, B16 = 1.039E-28

Surface 7: Am2 = -2.3702E-01, Am4 = 5.2751E-08, Am6 = -2.0673E-13 Am8 = 6.1916E-16, Am10 = -2.1272E-18 B1 = 1.1285E-05, B3 = 8.2414E-09, B5 = -8.3701E-12 B7 = 1.6093E-15, B9 = 1.0336E-19

Surface 8: Am2 = -9.0813E + 00, Am4 = -1.3697E-10, Am6 = -1.0361E-12 Am8 = -1.5020E-16, Am10 = -1.2669E-21, Am12 = -4.0301 E-25 Am14 = 5.7340E-30, Am16 = 1.6885E-33 B1 = 1.5474E-06, B3 = 2.8010E-10, B5 = -1.2492E-13 B7 = 2.5220E-17, B9 = -3.6112E- 21, B11 = 2.9135E-25 B13 = -1.6452E-29, B15 = 1.7857E-33, B17 = -1.0747E-37

Ninth surface: Am2 = -7.4453E + 00, Am4 = -7.0557E-08, Am6 = 1.9461E-13 Am8 = -1.3606E-16, Am10 = -5.2312E-21, Am12 = -2.0517E -29 Am14 = -2.4196E-34 B2 = -1.1619E-08, B4 = -2.2670E-11, B6 = -1.5740E-15 B8 = -4.5789E-20, B10 = -3.8438E-24, B12 = -7.4648E-28 B14 = -5.8757E-32, B16 = 1.1024E-36, B18 = 1.5980E-40 C0 = -3.1492E-01 I0 = 3.1657E-06, I1 = -1.3699E-09, I2 = 1.2086E-10 I3 = 4.1379E-12, I4 = 3.0682E-13, I5 = -7.2697E-15 I6 = -1.1934E-16, I7 = 4.3896E-18, I8 = 1.3145E-20 I9 = -1.2026 E-21, I10 = -2.1378E-24, I11 = 1.7132E-25 I12 = 7.8714E-28, I13 = -1.3127E-29, I14 = -1.2411E-31 I15 = 5.1005E-34, I16 = 8.2218 E-36, I17 = -7.8048E-39 I18 = -1.9700E-40 K0 = 3.3658E-08, K1 = 5.7068E-11, K2 = -1.1867E-11 K3 = -1.6517E-13, K4 =- 6.3184E-15, K5 = 3.0942E-16 K6 = -1.4550E-18, K7 = -1.9660E-19, K8 = 3.004 5E-21 K9 = 5.6936E-23, K10 = -9.5063E-25, K11 = -8.6717E-27 K12 = 1.364E-28, K13 = 7.2210E-31, K14 = -1.0155E-32 K15 = -3.1157 E-35, K16 = 3.8226E-37, K17 = 5.4542E-40 K18 = -5.7217E-42

[0031]

As described above, in the optical scanning device according to the first aspect, the correction optical system includes at least a resin lens having an anamorphic surface having negative power in both the main scanning direction and the sub-scanning direction. It has at least one pair of a glass lens having an anamorphic surface having a positive power in the sub-scanning direction, and is provided between the coupling optical system and the deflecting / reflecting surface. Optimal determination of the temperature dependence of the curvature, linear expansion coefficient, and refractive index of the anamorphic surface of the lens for correction in order to properly correct the imaging position deviation in the main scanning direction and the imaging position deviation in the sub-scanning direction. Accordingly, it is possible to correct a focus position shift due to a change in environment (temperature and humidity) in both the main scanning direction and the sub-scanning direction. Also, by using the anamorphic surface, the opposing surface can be made flat, so that it can be used as a mounting reference surface, and the occurrence of eccentricity that degrades optical performance is suppressed.

According to a second aspect of the present invention, in addition to the configuration of the first aspect, a correction optical system including a resin lens having an anamorphic surface and a glass lens having an anamorphic surface is integrally held by a holding member. By doing so, the wavefront aberration that occurs in the correction optical system can be suppressed in advance during assembly adjustment. In the optical scanning device according to the third aspect, in addition to the configuration of the second aspect, the correction optical system integrated by the holding member has a structure that can be moved and adjusted in the optical axis direction. When assembling in the optical system unit, the focal position shift in the main / sub-scanning direction can be adjusted in advance. In the optical scanning device according to the fourth aspect, in addition to the configuration of the second aspect, the correction optical system integrated by the holding member has a structure capable of rotating and adjusting in a direction perpendicular to the optical axis, so that the correction is performed. It is possible to adjust the entire optical system while maintaining the wavefront aberration in the optical system. In the optical scanning device according to the fifth aspect, the first, second, and third aspects of the invention are described.
Alternatively, in addition to the configuration of 4, at least one of the anamorphic surfaces of the correction optical system is formed of an aspheric surface in both the main and sub-scanning directions, so that the wavefront aberration can be satisfactorily corrected. In the optical scanning device according to the sixth aspect, in addition to the configuration of the first, second, third, fourth, or fifth aspect, a surface distance between a resin lens having an anamorphic surface and a glass lens having an anamorphic surface is L, When the focal length of the entire correction optical system in the sub-scanning direction is fs, the condition: 0 <L
By satisfying /fs<0.1, it is possible to satisfactorily correct the wavefront aberration and obtain a small-diameter light spot.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an embodiment of the present invention, and is an explanatory view of an optical arrangement in which an arrangement of an optical system constituting an optical scanning device is developed on a main scanning plane.

2A and 2B are explanatory diagrams of an optical system arrangement on an optical path from a light source to a deflecting / reflecting surface of the optical scanning device shown in FIG. 1, wherein FIG. 2A is an optical path diagram developed on a plane in a main scanning direction, and FIG. FIG. 4 is an optical path diagram developed on a plane in the sub-scanning direction.

FIG. 3 is a perspective view illustrating an example of a configuration in which lenses of a correction optical system are integrated.

FIG. 4 is a diagram showing field curvature and constant velocity characteristics when the scanning image forming optical system shown in the embodiment is used.

FIG. 5 is a diagram illustrating wavefront aberrations when a toroidal surface is used as an anamorphic surface of a correction optical system and when a special toroidal surface is used.

[Explanation of symbols]

 1: light source 2: coupling lens 3: correction optical system 3a: resin correction lens 3b: glass correction lens 3c: correction optical system unit 3d: pedestal 4: plane mirror 5: optical deflector (polygon mirror) 5a: deflection reflection Surface 6: Scanning optical system 6a, 6b: Scanning lens 7: Scanned surface

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiromichi Atsumi 1-3-6 Nakamagome, Ota-ku, Tokyo, Ricoh Co., Ltd. (72) Inventor Koji Sakai 1-3-6 Nakamagome, Ota-ku, Tokyo No./F-term in Ricoh Co., Ltd. (Reference) 2H045 AA01 CA34 CA44 CA54 CA67 CB04

Claims (6)

[Claims] 1. A light source for emitting a light beam, a coupling optical system for converting a light beam from the light source into a parallel light beam, a substantially convergent light beam, or a substantially divergent light beam, and coupling to a subsequent optical system; A light deflector that reflects light beams from the system on a deflecting / reflecting surface to deflect and scan, a scanning image forming optical system that condenses the light beams deflected by the light deflector as a light spot on a surface to be scanned, and environmental fluctuations. An optical scanning device comprising a correction optical system for self-correcting the focal position shift of the light spot on the surface to be scanned, wherein the correction optical system has an anamorphic having negative power in both the main scanning direction and the sub-scanning direction. A resin lens having a surface,
An optical scanning device comprising at least one pair of a glass lens having an anamorphic surface having at least a positive power in a sub-scanning direction, and being provided between the coupling optical system and the deflecting reflection surface. 2. The optical scanning device according to claim 1, wherein a correction optical system comprising a resin lens having an anamorphic surface and a glass lens having an anamorphic surface is integrally held by a holding member. . 3. The optical scanning device according to claim 2, wherein the correction optical system integrated by the holding member has a structure capable of adjusting the movement in the optical axis direction. 4. The optical scanning device according to claim 2, wherein the correction optical system integrated by the holding member has a structure capable of rotating and adjusting in a direction perpendicular to the optical axis. 5. The optical scanning device according to claim 1, wherein at least one of the anamorphic surfaces of the correction optical system is formed as an aspheric surface in both the main and sub scanning directions. Scanning device. 6. The optical scanning device according to claim 1, wherein the distance between the resin lens having the anamorphic surface and the glass lens having the anamorphic surface is L, and the entire distance of the correction optical system is set. The focal length in the sub-scanning direction is fs
Wherein the optical scanning device satisfies the following condition: 0 <L / fs <0.1.