JP2006221118A - Laser scanner and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a novel laser scanner that effectively reduces and prevents by a diffractive face a variation of optical characteristics due to a wavelength fluctuation of a semiconductor laser. <P>SOLUTION: The laser scanner is equipped with: a semiconductor laser 1; a coupling optical system 2 for coupling a luminous flux from the semiconductor laser 1; a first optical system 4 for guiding the luminous flux from the coupling optical system 2 to a light deflector; the light deflector 5 for deflecting the laser luminous flux from the first optical system 4 to the main scanning direction; and scanning optical systems 6, 7 for converging the laser luminous flux deflected by the light deflector 5 toward a surface to be scanned. The coupling optical system 2 is provided with a diffractive face having the same power in the main scanning direction and a subscanning direction. The first optical system 4 is provided with a diffractive face having a power only in the subscanning direction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a laser scanning device and an image forming apparatus.

  The present invention can be implemented as an optical scanning device such as a digital copying machine, a laser printer, a laser plotter, and a laser facsimile, and an image forming apparatus using the same.

  In recent years, in an image forming apparatus such as a digital copying machine or a laser printer, the density of image formation by optical scanning is increasing, and there is a demand for reducing the diameter of the light spot on the photosensitive member. In addition, it is also desired to promote the use of “lenses constituting the optical scanning device” as a resin in order to reduce costs.

  A semiconductor laser is generally used as the light source used in the optical scanning device, but it is known that “the wavelength of the laser light emitted from the semiconductor laser fluctuates due to a temperature change”. When the emission wavelength of the semiconductor laser fluctuates, the refractive index of the optical system that constitutes the optical scanning device fluctuates with the fluctuation of the wavelength, and the imaging performance changes, so that “the converging position of the laser beam that scans the scanned surface” Deviates from the surface to be scanned, and the light spot diameter increases.

  Temperature fluctuations in the optical scanning device also cause fluctuations in the optical characteristics of optical elements such as lenses. For example, in the case of lenses, temperature fluctuations cause the lens to expand or contract, and accordingly the curvature of the lens surface and lens flesh. The thickness changes and the refractive index of the lens material also changes. Such a change in the optical element also causes an increase in the light spot diameter.

If the light spot diameter increases in this way, the desired recording density cannot be achieved.
The above-mentioned problem occurs when the optical element constituting the optical scanning device is a glass lens or a resin lens. In particular, in a resin lens, the lens surface accompanying expansion / contraction due to temperature fluctuations. The curvature, lens thickness variation, and refractive index variation of the lens material are also remarkable, and the above problem is also serious.

  As a method for coping with fluctuations in the emission wavelength of the semiconductor laser, a diffractive surface is arranged on the light source side of the optical deflector, and a diffractive surface is also arranged on the scanning optical system that converges the deflected light beam toward the scanned surface. There is known a method for reducing / compensating for fluctuations in “condensing position of a light beam that scans a surface to be scanned” by a change in diffraction angle associated with wavelength fluctuations (Patent Document 1).

  Although this method is considered to be effective, the “scanning optical system that converges the deflected light beam toward the scanning surface” is generally a large lens that is long in the main scanning direction, and the effective scanning region of such a large lens. If a diffractive surface is to be formed, the diffractive surface has a large area, so that processing of the diffractive surface takes time, and the manufacturing efficiency of the lens on which the diffractive surface is formed is low, resulting in an increase in cost.

  Also, by using a diffractive optical surface as the lens surface of the collimating lens that converts the divergent laser beam emitted from the semiconductor laser into a parallel beam, the “laser beam that scans the surface to be scanned is associated with fluctuations in the emission wavelength of the semiconductor laser. Patent Document 2 proposes to correct the “condensation position fluctuation”. In a laser scanning device, it is common to include “anamorphic optical elements having different imaging effects in the main scanning direction and the sub-scanning direction” among the optical elements arranged between the light source and the surface to be scanned. In general, the image forming action in the laser scanning device is different between the main scanning direction and the sub-scanning direction. In the method described in Patent Document 2, since the diffractive optical surface formed on the collimating lens is rotationally symmetric with respect to the optical axis, the influence of fluctuations in the emission wavelength of the semiconductor laser can be corrected independently in the main scanning direction and the sub-scanning direction. I can't.

Japanese Patent No. 3397683 JP 2000-171741 A

  In view of the circumstances as described above, the present invention realizes a novel laser scanning device capable of effectively reducing and preventing fluctuations in optical characteristics due to wavelength fluctuations of a semiconductor laser by means of a diffraction surface, and provides a good image using this laser scanning device. An object is to realize an image forming apparatus capable of forming images.

The laser scanning device according to the present invention includes a semiconductor laser, a coupling optical system, a first optical system, an optical deflector, and a scanning optical system.
The “semiconductor laser” emits a laser beam for optical scanning.
The “coupling optical system” couples a divergent laser beam from a semiconductor laser and converts it into a beam form suitable for the subsequent optical system.

The “first optical system” is an optical system that guides the light beam from the coupling optical system to the optical deflector.
The “optical deflector” deflects the laser beam from the first optical system in the main scanning direction.
The “scanning optical system” condenses the laser beam deflected by the optical deflector toward the surface to be scanned.

The laser scanning device according to claim 1 has the following characteristics.
That is, the coupling optical system has “a diffractive surface having the same power in the main scanning direction and the sub-scanning direction”, and the first optical system has “a diffractive surface having power only in the sub-scanning direction”.
In order to arrange the diffractive surface in the coupling optical system, for example, at least one of the lenses constituting the coupling optical system should have “a diffractive surface having the same power in the main scanning direction and the sub-scanning direction”. In order to arrange the diffractive surface in the first optical system, for example, at least one lens constituting the first optical system should have a “diffraction surface having power only in the sub-scanning direction”. Good.

  The coupling action of the coupling optical system in the laser scanning device according to claim 1 can be made to be a collimating action so that “substantially parallel light is emitted from the coupling optical system” (claim 2).

  3. The laser scanning device according to claim 1, wherein the coupling optical system may have a “refractive surface having a positive power” (claim 3). That is, in this case, the coupling optical system includes a “diffractive surface having the same power in the main scanning direction and the sub-scanning direction” and a “refractive surface having a positive power”.

  The coupling optical system in the laser scanning device according to claim 1, 2 or 3 may have a “resin lens having a diffractive surface having a positive power” (claim 4). When the coupling optical system is configured as a lens system, the coupling lens can be configured as a single lens or a plurality of lenses.

  The first optical system in the laser scanning device according to any one of claims 1 to 4 can include a “resin lens having a diffractive surface having a positive power in the sub-scanning direction” (claim 5). When the first optical system is configured as a lens system, the first optical system can be configured by a single lens or a plurality of lenses.

  6. The laser scanning device according to claim 1, wherein the first optical system can have a "refractive surface having a negative power in the sub-scanning direction" (claim 6). That is, the first optical system can have only a diffractive surface, or can have a refracting surface together with the diffractive surface.

  A laser scanning device according to a seventh aspect includes a semiconductor laser, a coupling optical system, a first optical system, an optical deflector, and a scanning optical system.

The “semiconductor laser” emits a laser beam for optical scanning.
The “coupling optical system” couples a divergent laser beam from a semiconductor laser and converts it into a beam form suitable for the subsequent optical system.

The “first optical system” is an optical system that guides the light beam from the coupling optical system to the optical deflector.
The “optical deflector” deflects the laser beam from the first optical system in the main scanning direction.
The “scanning optical system” condenses the laser beam deflected by the optical deflector toward the surface to be scanned.

  The laser scanning device according to claim 7, wherein “the lens constituting the first optical system has a diffractive surface having power only in the sub-scanning direction and a refracting surface having negative power in the sub-scanning direction”. And

  The laser scanning device according to any one of claims 1 to 7, comprising a "first holding member for holding a semiconductor laser and a coupling optical system", wherein the position of the coupling optical system is adjusted at least in the optical axis direction. It can be configured to be fixed to the first holding member later.

  The laser scanning device according to claim 8 has “a second holding member that holds at least the first holding member and the first optical system”, and the first after the coupling optical system is fixed to the first holding member. The optical system can be configured to be fixed to the second holding member after being adjusted at least in the optical axis direction.

  The laser scanning device according to any one of claims 1 to 9, wherein the diffractive surface of the coupling optical system is “rotationally symmetric about the optical axis”, and the diffractive surface of the first optical system is “in the sub-scanning direction”. It can be a “diffractive surface on which gratings are arranged” (claim 10).

  The laser scanning device according to any one of claims 1 to 10 may be configured such that the scanning optical system includes at least one resin lens. Of course, all the refractive optical elements arranged on the optical path from the semiconductor laser as the light source to the surface to be scanned can be glass lenses, or a part can be glass lenses and the rest can be resin lenses. Furthermore, all can be made into a resin lens.

  The laser device according to any one of claims 1 to 11 can be implemented as a single-beam scanning device, or a semiconductor laser (semiconductor laser array or a plurality of semiconductor lasers having a light source having two or more laser light emitting units). It is also possible to implement as a “multi-beam scanning type scanning device” using a semiconductor laser.

  An image forming apparatus of the present invention uses any one of the laser scanning devices according to claims 1 to 11 (claim 12). Such an image forming apparatus can be implemented as a digital copying machine, a laser printer, a laser facsimile, a laser plotter, or the like.

  The image forming apparatus can be implemented as a monochrome image, or can be configured to form a multicolor or color image. In other words, various types of conventionally known image forming apparatuses can be used.

  As described above, the laser scanning device of the present invention does not provide a diffractive surface for correcting the emission wavelength variation of the semiconductor laser in the scanning optical system having a large lens area. Compared to low cost.

  In the laser scanning device according to claim 1, the coupling optical system has “a diffractive surface having the same power in the main scanning direction and the sub-scanning direction”, and the first optical system has power only in the sub-scanning direction. Since it has a “diffraction surface”, it is possible to independently correct the influence of fluctuations in the emission wavelength of the semiconductor laser in the main scanning direction and the sub-scanning direction.

  Further, although the diffractive surface is extremely sensitive to wavelength fluctuations, the lens constituting the first optical system is “a diffractive surface having power only in the sub-scanning direction” as in the laser scanning device according to claim 7. By having a refracting surface having a negative power in the sub-scanning direction, the action of the first optical system can be “shared between the refracting surface and the diffractive surface”, and the correcting action of the diffractive surface is excessive. Can effectively be avoided.

  Therefore, the laser scanning device of the present invention can effectively correct the influence of the emission wavelength variation of the semiconductor laser and can be realized at low cost. An image forming apparatus using such a laser scanning device can realize stable image formation against environmental fluctuations.

  Hereinafter, embodiments of the present invention will be described. First, a general optical system determines how much the condensing position of a laser beam that scans a surface to be scanned is shifted with respect to the surface to be scanned due to the influence of a temperature change. The configuration will be described.

FIG. 1 shows a general optical configuration of a laser scanning device.
In FIG. 1, reference numeral 1 is a semiconductor laser used as a light source, reference numeral 2 is a coupling lens, reference numeral 3 is an aperture for beam shaping, reference numeral 4 is an anamorphic lens which is a “first optical system”, and reference numeral 5 is “ Polygon mirror which is an “optical deflector”, reference numerals 6 and 7 are scanning lenses constituting a “scanning optical system”, reference numeral 8 is dust-proof glass, and reference numeral 9 is a surface to be scanned. The photosensitive surface. Reference numeral 10 denotes a soundproof glass.

  In this example, the semiconductor laser 1 has a cover glass with a thickness of 0.3 mm, and emits a divergent laser beam through the cover glass. The laser beam emitted from the semiconductor laser 1 is suppressed in the divergence by the coupling lens 2 to become a “weakly divergent laser beam”. “Parallel light flux in the main scanning direction” and “light flux that converges linearly in the vicinity of the deflection reflection surface of the polygon mirror 5” in the sub-scanning direction.

  The laser beam reflected by the deflecting and reflecting surface of the polygon mirror 5 becomes a deflected laser beam that is deflected at a constant angular velocity by the constant speed rotation of the polygon mirror 5, passes through the scanning lenses 6 and 7 forming the scanning optical system, and is dust-proof glass. 8 is guided to the surface 9 to be scanned, is condensed as a light spot on the surface 9 to be scanned by the imaging action of the scanning lenses 6 and 7, and scans the surface 9 to be scanned.

Specific examples of such a laser scanning device are given below.
Semiconductor laser 1
Emission wavelength: 780.1 nm (25 ° C.), 786.5 nm (45 ° C.)
Coupling lens 2
Incident side shape: coaxial aspherical surface expressed by the following formula (1)
x = (h ² / R) / [1 + √ {1- (1 + K) (h / R) ² }] + A4 ・ h ⁴ + A6 ・ h ⁶ + A8 ・ h ⁸ + A10 ・ h ¹⁰・・ (1)
Here, h: distance from the optical axis, R: paraxial radius of curvature, K: conic constant, A4, A6, A8, A10: higher order coefficients, x: depth in the optical axis direction.

R, K, A4, A6, A8, A10 values
R = 86.09118
K = 361.987634
A4 = -0.827025E-04
A6 = -0.413360E-05
A8 = 0.942600E-06
A10 = -0.936986E-07
In the above notation, for example, “-0.936986E-07” represents “-0.936986 × 10 ⁻⁷ ”. The same applies to the following.

Ejection side: Coaxial aspherical surface represented by the formula (1)
R, K, A4, A6, A8, A10 values
R = -8.71000
K = -0.310240
A4 = 0.592273E-04
A6 = 0.250465E-06
A8 = 0.119847E-06
A10 = -0.563217E-08.

Anamorphic lens 4
Incident side shape: Anamorphic surface expressed by the following formula (2)
x = {(1 / Rm) ・ y ² + (1 / Rs) ・ z ² } / [1 + √ {1- (y / Rm) ^2- (z / Rs) ² }] ・ ・ (2)
Here, y: distance in the main scanning direction from the optical axis, z: distance in the sub scanning direction, Rm: radius of curvature in the main scanning direction, Rs: radius of curvature in the sub scanning direction, and x: depth in the optical axis direction.

Rm and Rs values
Rm = 500
Rs = 35.83
Injection side shape: plane.

Scanning lens 6
Incident side surface shape: coaxial aspherical surface represented by the above formula (1)
R, K, A4, A6, A8, A10 values
R = -312.6
K = 2.667
A4 = 1.79E-07
A6 = -1.08E-12
A8 = -3.18E-14
A10 = 3.74E-18.

Injection side shape: coaxial aspherical surface represented by the above formula (1)
R, K, A4, A6, A8, A10 values
R = -83.0
K = 0.02
A4 = 2.50E-07
A6 = 9.61E-12
A8 = 4.54E-15
A10 = -3.03E-18
The vertices on both sides of the scanning lens 6 are shifted by 1.16 mm upward in the figure with respect to the principal ray in FIG.

Scanning lens 7
Incident side surface shape: a non-circular arc represented by the following equation (3) with respect to the main scanning direction, and a “curvature radius in the sub-scanning direction” continuously with respect to the sub-scanning direction as represented by the following equation (4). Change.

x = (y ² / Rm) / [1 + √ {1- (1 + K) (y / Rm) ² }] + A4 ・ y ⁴ + A6 ・ y ⁶ + A8 ・ y ⁸ + A10 ・ y ¹⁰・・ (3)
Here, y: main scanning direction distance from the optical axis, Rm: paraxial radius of curvature in the main scanning direction, K: conic constant, A4, A6, A8, A10: higher order coefficients, x: depth in the optical axis direction It is.

Rs (y) = Rs + Σbj · y ^j (j = 1, 2, 3,...) (4)
Where, y: distance in the main scanning direction from the optical axis, Rs (y): radius of curvature in the sub-scanning direction at a distance y in the main scanning direction from the optical axis, Rs: sub-scanning radius on the optical axis, bj : The following coefficients (j = 1, 2, 3,...).

Values of Rm, Rs, K, A4, A6, A8, A10, b2, b4, b6, b8, b10, b12
Rm = -500
K = -71.73
A4 = 4.33E-08
A6 = -5.97E-13
A8 = -1.28E-16
A10 = 5.73E-21
Rs = -47.7
b2 = 1.60E-03
b4 = -2.32E-07
b6 = 1.60E-11
b8 = -5.61E-16
b10 = 2.18E-20
b12 = -1.25E-24.

  Injection side shape: Toroidal surface. The shape in the sub-scanning direction is an arc represented by the following formula (5), and is a shape rotated around an “axis parallel to the sub-scanning direction” separated from the vertex of the arc by Rm in the optical axis direction.

x = (z ² / Rs) / [1 + √ {1- (z / Rs) ² }] (5)
Where y: distance in the main scanning direction from the optical axis, Rs: paraxial radius of curvature in the sub-scanning direction, and x: depth in the optical axis direction.

Rm and Rs values
Rm = -1000
Rs = -23.38
Also, the vertices on both sides are shifted by 1.21 mm upward in the figure with respect to the principal ray in FIG.

  When the surface intervals are determined as shown in FIG. 2 (for the sake of simplicity, each lens is drawn as a block), the values of these surface intervals: d1 to d10 are as follows.

d1 = 12.843
d2 = 3.8
d3 = 102.8
d4 = 3.0
d5 = 69.3
d6 = 51.7
d7 = 31.4
d8 = 78.0
d9 = 3.5
d10 = 143.62.

In the specific example in the description, as shown in FIG. 1, a dust-proof glass 8 having a thickness of 1.9 mm (25 ° C.) is inserted. The refractive index of the material of the dustproof glass 8 is 1.511161 at a light wavelength: 780.1 nm (temperature: 25 ° C.), 1.511161 at a light wavelength: 786.5 nm (temperature: 45 ° C.), and a linear expansion coefficient: 7. 5E-06K- ¹ . In this example, the soundproof glass 10 is not used.
The semiconductor laser 1 and the coupling lens 2 are fixed to the same member made of aluminum. The linear expansion coefficient of this holding member is 4.0E-05K- ¹ .

All of the above lenses are made of “the same resin material”. The refractive index of this resin is 1.523946 at a light wavelength: 780.1 nm (temperature: 25 ° C.), and a light wavelength: 786.5 nm (temperature: 45 ° C.). 1.522105 and linear expansion coefficient: 7.0E-05K- ¹ .

  Under the above conditions, the focus position (laser beam condensing position) with respect to the scanned surface 9 is calculated in consideration of changes in the emission wavelength, refractive index, surface shape, and wall thickness due to temperature changes as follows. Become.

Temperature Focus position
Main scanning direction Sub scanning direction 25 ° C 0.0mm 0.0mm
45 ° C 11.6mm 3.3mm
As can be seen from this result, when the environmental temperature changes from 25 ° C. to 45 ° C., the condensing position of the laser beam that scans the scanned surface changes significantly with respect to the scanned surface.

  Hereinafter, specific examples in which the present invention is implemented with respect to the optical configuration described with reference to FIGS. 1 and 2 will be described.

  In Example 1, the emission wavelength of the semiconductor laser 1 was 655 nn and 659 nm at temperatures of 25 ° C. and 45 ° C., respectively.

Coupling lens 2
Incident side shape: Diffraction surface by concentric grating
The phase function of this diffractive surface: φ (h) is expressed by the following equation (6).
φ (h) ＝ C1 ・ h ²・ ・ （６）
Here, h: distance from the optical axis, C1: phase coefficient.
Phase coefficient: C1 value
C1 = -1.1270E-02
FIG. 3A is an explanatory view showing a “diffractive surface by a concentric grating” on the incident side surface of the coupling lens 2. This diffractive surface has “positive power”.

Injection side shape: aspherical surface represented by the above formula (1)
R, K, A4, A6, A8, A10 values
R = -34.32865 K = -71.517137
A4 = -0.208422E-03
A6 = 0.651475E-05
A8 = -0.238199E-06
A10 = 0.770435E-08
The exit side is a positive power refracting surface.
In the first embodiment, the coupling lens 1 sets “a divergent laser beam from the semiconductor laser 1 as a substantially parallel beam”.

1st lens 4
Incident side surface shape: no curvature in the main scanning direction and a non-arc shape represented by the following equation (7) in the sub-scanning direction.

x = (z ² / Rs) / [1 + √ {1- (1 + K) (z / Rs) ² }] + B4 ・ z ⁴ + B6 ・ z ⁶ + B8 ・ z ⁸ + B10 ・ z ¹⁰・・ (7)
Where, z: distance in the sub-scanning direction from the optical axis, Rs: paraxial radius of curvature in the sub-scanning direction, K: conic constant, B4, B6, B8, B10: higher-order coefficients, x: in the optical axis direction Depth.

Rs, K, B4, B6, B8, B10 values
Rs = -54.46507
K = -0.072542
B4 = 0.577350E-07
B6 = 0.474038E-07
B8 = -0.190253E-07
B10 = 0.247352E-08
The incident side surface of the first lens 4 has a negative power only in the sub-scanning direction.

Emitting side shape: diffractive surface with grating in the sub-scanning direction
The phase function of the diffractive surface: φ (z) is expressed by the following equation (8).
φ (z) ＝ C1 ・ z ²・ ・ (8)
Here, z: distance in the sub-scanning direction from the optical axis, and C1: phase coefficient.

Phase coefficient: C1 value
C1 = -8.8148E-03
FIG. 3B illustrates the “diffractive surface having a grating in the sub-scanning direction” formed on the exit side surface of the first lens 4 in an explanatory manner. This diffractive surface has a positive power only in the sub-scanning direction.
Accordingly, the first lens 4 focuses the parallel light flux from the coupling lens 2 side only in the sub-scanning direction, and focuses it “long in the main scanning direction” near the deflection reflection surface of the polygon mirror 5.

Scanning lens 6
Incident side surface shape: The surface shape in the main scanning plane has a non-arc shape represented by the following formula (8), and the curvature in the sub-scanning direction changes according to the distance in the main scanning direction according to the attachment (9).
x = (y ² / Rs) / [1 + √ {1- (1 + K) (y / Rs) ² }] + A4 ・ y ⁴ + A6 ・ y ⁶ + A8 ・ y ⁸ + A10 ・ y ¹⁰・・ (8)
Where y: distance in the main scanning direction from the optical axis, Rm: paraxial radius of curvature in the main scanning direction, K: conic constant, A4, A6, A8, A10...: Higher order coefficient, x: optical axis The depth of direction.

Cs (Y) = 1 / Rs (0) + B1 ・ Y + B2 ・ Y ² + B3 ・ Y ³ + B4 ・ Y ⁴ + B5 ・ Y ⁵ + ・ ・ (9)
Here, Y: distance in the main scanning direction from the optical axis, Cs (Y): curvature in the sub-scanning direction, K: conical constant, B1, B2, B3, B4, B5...: Higher order coefficients.

Rm, Rs, K, A4, A6, A8, A10, A12, B1, B2, B3, B4, B5
Rm = -279.9, Rs = -61.
K = -2.900000E + 01
A4 = 1.755765E-07
A6 = -5.491789E-11
A8 = 1.087700E-14
A10 = -3.183245E-19
A12 = -2.635276E-24
B1 = -2.066347E-06
B2 = 5.727737E-06
B3 = 3.152201E-08
B4 = 2.280241E-09
B5 = -3.729852E-11
B6 = -3.283274E-12
B7 = 1.765590E-14
B8 = 1.372995E-15
B9 = -2.889722E-18
B10 = -1.984531E-19
The image side surface shape is an aspherical surface represented by the formula (9), and the coefficients are as follows.

R = -83.6
K -0.549157
B4 = 2.748446E-07
B6 = -4.502346E-12
B8 = -7.366455E-15
B10 = 1.803003E-18
B12 = 2.727900E-23.

Scanning lens 7
Incident side shape:
The main scanning direction is a non-circular shape represented by the formula (8).
The shape in which the curvature in the sub-scanning direction changes according to the above equation (9) according to the distance in the main scanning direction from the optical axis
Rm, Rs, K, A4, A6, A8, A10, ..., B1, B2, B3, B4, B5 ...
Rm = 6950, Rs = 110.9
K = 0.000000E + 00
A4 = 1.549648E-08
A6 = 1.292741E-14
A8 = -8.811446E-18
A10 = -9.182312E-22
B1 = -9.593510E-07
B2 = -2.135322E-07
B3 = -8.079549E-12
B4 = 2.390609E-12
B5 = 2.881396E-14
B6 = 3.693775E-15
B7 = -3.258754E-18
B8 = 1.814487E-20
B9 = 8.722085E-23
B10 = -1.340807E-23.

Emitting side surface shape: The surface shape in the main scanning plane is a non-arc shape represented by the above equation (8), and the curvature in the sub-scanning direction changes according to the above equation (9) according to the distance in the main scanning direction from the optical axis. Shape to
Rm, Rs, K, A4, A6, A8, A10, ..., B1, B2, B3, B4, B5 ...
Rm = 766, Rs = -68.22
K = 0.000000E + 00
A4 = -1.150396E-07
A6 = 1.096926E-11
A8 = -6.542135E-16
A10 = 1.984381E-20
A12 = -2.411512E-25
B2 = 3.644079E-07
B4 = -4.847051E-13
B6 = -1.666159E-16
B8 = 4.534859E-19
B10 = -2.819319E-23.

  The values of the plane spacings d1 to d10 determined as shown in FIG. 2 are as follows.

d1 = 26.07144
d2 = 3.8
d3 = 102.8
d4 = 3.0
d5 = 121.7448
d6 = 64.00685
d7 = 22.6
d8 = 75.85
d9 = 4.9
d10 = 158.71
In Example 1, as shown in FIG. 1, a soundproof glass 10 and a dustproof glass 8 having a thickness of 1.9 mm (25 ° C.) are inserted. The refractive indexes of these glasses are 1.514371 at a light wavelength: 655 nm (temperature: 25 ° C.), 1.514291 at a light wavelength: 659 nm (temperature: 45 ° C.), and a linear expansion coefficient: 7.5E-06K ⁻¹ . .

All the lenses are made of the same resin material. The refractive index of this resin is 1.527257 at a light wavelength: 655 nm (temperature: 25 ° C.), 1.525368 at a light wavelength: 659 nm (temperature: 45 ° C.), and a linear expansion coefficient: 7.0E-05K ⁻¹ .

The semiconductor laser 1 and the coupling lens 2 are fixed to the same member (holding member) made of aluminum, and the linear expansion coefficient of the holding member is 4.0E-05K- ¹ .

  Under the above conditions, the focus position (laser beam condensing position) with respect to the scanned surface 9 is calculated in consideration of changes in emission wavelength, refractive index, surface shape, and thickness with temperature.

Temperature Focus position
Main scanning direction Sub scanning direction 25 ° C 0.0mm 0.0mm
45 ° C 0.0mm 0.0mm
From this result, it can be seen that in the laser scanning device of Example 1, the focus position does not vary substantially even when the environmental temperature changes from 25 ° C. to 45 ° C. This effect is due to the use of a diffractive surface.

  The above-described first embodiment is a single-beam laser scanning device, but a “multi-beam method” is used by combining a light beam from a plurality of semiconductor lasers with a prism or the like or using a semiconductor laser array. Is also possible.

  The laser scanning apparatus according to the first embodiment described above includes a semiconductor laser 1, a coupling optical system 2 for coupling a light beam from the semiconductor laser, and a first light beam for guiding the light beam from the coupling optical system to an optical deflector. 1 optical system 4, an optical deflector 5 for deflecting the laser beam from the first optical system in the main scanning direction, and scanning for condensing the laser beam deflected by the optical deflector toward the scanning surface 9 A laser scanning device including optical systems 6 and 7, wherein the coupling optical system 2 has a diffractive surface (a diffractive surface formed by concentric circular gratings) having the same power in the main scanning direction and the sub-scanning direction. The optical system 4 has a “diffraction surface having power only in the sub-scanning direction”.

  The coupling optical system 2 emits substantially parallel light (Claim 2), has a refracting surface (exit side) having positive power (Claim 3), and has a diffractive surface (incident side) having positive power. (Claim 4).

  The diffractive surface is “the direction of refraction angle change due to wavelength change is opposite to that of a normal refracting surface”. Therefore, by assigning “a part of the positive power” of the entire optical system to the diffractive surface, the “focus position shift due to temperature change” that occurs because the coupling lens 2 itself is a resin, as well as the optical system. It is possible to correct a focus position shift caused by a temperature change caused by another resin lens.

  However, if only the diffractive surface bears the positive power of the coupling optical system, it becomes too sensitive to changes in wavelength, so it is desirable to have a refractive surface with positive power. In addition, since the diffractive surface has the same power in the main scanning direction and the sub-scanning direction on the surface on the light source side, there is an advantage that performance degradation hardly occurs even when the coupling lens 2 is rotated with respect to the optical axis.

  The first lens 4 that is the first optical system is a resin lens having a diffractive surface (exit side surface) having a positive power in the sub-scanning direction and has a negative power in the sub-scanning direction. It has a refracting surface (incident side surface).

  The laser scanning apparatus according to the first embodiment also includes a semiconductor laser 1, a coupling optical system 2 that couples a laser beam from the light source, and a first optical that guides the laser beam from the coupling optical system to an optical deflector. System 4, optical deflector 5 for deflecting the laser beam from the first optical system in the main scanning direction, and scanning optical system 6 for condensing the laser beam deflected by the optical deflector toward the surface to be scanned , 7 in which the lens constituting the first optical system 4 has a diffractive surface (exit side surface) having power only in the sub-scanning direction and negative power in the sub-scanning direction. It has a refracting surface (incident side surface).

  In the first lens 4 as the first optical system, in Example 1, a “refractive surface having negative power only in the sub-scanning direction” is formed on the incident-side surface, and “sub-scanning direction” is formed on the exit-side surface. Only a diffractive surface having a positive power ”is provided. The “focus position shift in the main scanning direction” due to the temperature change can be corrected by the diffractive surface provided in the coupling lens 2. However, in the laser scanning device of the embodiment, the positive power of the entire optical system is Since the scanning direction is stronger than the main scanning direction, in order to correct the focus position shift due to temperature changes in the sub-scanning direction, a “diffractive surface with positive power in the sub-scanning direction” is further required. In Example 1, the “diffractive surface having power only in the sub-scanning direction” provided on the exit side surface of the first lens 4 is used.

  The power of the entire first lens 4 is determined from “a target value for the spot diameter of the light spot”, and the value is “a positive power of the diffractive surface necessary for correcting a focus position shift due to a temperature change in the sub-scanning direction. Is smaller than Therefore, the refracting surface of the first lens 4 is set to a negative power, and the power of the entire first lens 4 is set to an appropriate value while ensuring the positive power of the diffraction surface.

  In addition, the focal length of the entire system increases in the positive direction due to the temperature rise, whereas the concave surface extends in the negative direction due to thermal expansion, so that there is also an effect of reducing focus shift due to temperature change.

  As in Example 1, the lens having the diffractive surface (coupling lens 2 and first lens 4) is made of resin, so that a negative image of the grating on the diffractive surface is engraved in advance on the mold, and the grating is formed by injection molding or thermal transfer. The shape can be transferred, enabling mass production at low cost.

  FIG. 4 is a diagram for explaining a method of positioning the coupling lens 2 and the first lens 4.

  The semiconductor laser 1 as a light source is fixed to the first holding member 11 by press fitting or the like. Next, the coupling lens 2 is fixed to the first holding member 11 "after adjustment in the optical axis direction" (claim 8). This makes it possible to reliably convert “emitted light into a substantially parallel light beam” by the coupling lens 2 even if the light emitting point position varies with respect to the case of the semiconductor laser.

  In the example of FIG. 4, the first holding member 11 is integrated and the coupling lens 2 is fixed by adhesion. However, the first holding member 11 may be composed of a plurality of members or a cup. The fixing method of the ring lens 2 may be other than adhesion.

  The first holding member 11 to which the semiconductor laser 1 and the coupling lens 2 are fixed is fixed to the second holding member 12. Then, the position of the first lens 4 is adjusted at least in the optical axis direction and fixed to the second holding member 12 so that the focus position in the sub-scanning direction becomes a desired position. Since the first lens 4 has power only in the sub-scanning direction, the focus position in the main scanning direction does not change even if the optical axis direction of the first lens 4 is adjusted, and the main scanning direction and the sub-scanning direction are independent. Therefore, the adjustment is easy.

  In Example 1, the diffractive surface (incident side surface) of the coupling optical system 2 is rotationally symmetric with respect to the optical axis, and the diffractive surface (exit side surface) of the first optical system 4 has a grating in the sub-scanning direction. Lined diffraction surfaces (claim 10). The scanning optical system (scanning lenses 6 and 7) includes at least one resin lens.

  To supplement a little, the “diffractive surface” formed on the coupling lens 2 and the first lens 4 has a cross-sectional shape of the diffraction surface “a plane indicated by a broken line” as shown in FIG. However, a diffractive surface may be formed on a macroscopic curved surface indicated by a broken line as in the cross-sectional shape shown in FIG. In this way, it is possible to combine the refraction effect by the macroscopic curved surface indicated by the broken line and the “diffraction effect by the diffraction surface”.

  In the first embodiment, as described above, the coupling lens 2 uses the divergent laser beam from the semiconductor laser 1 as a substantially parallel beam. In this case, if the incident side surface of the first lens 4 has a planar shape, the reflected light component reflected by the incident side surface of the first lens 4 returns to the semiconductor laser 1 and is collected in the light emitting section as shown in FIG. It is conceivable to destabilize the light emitted from the semiconductor laser 1, but as in the first embodiment, the incident side surface of the first lens 4 is "a concave surface having negative power in the sub-scanning direction". Accordingly, it is possible to effectively prevent the reflected light from the incident side surface from being collected on the light emitting portion of the semiconductor laser 1 as shown in FIG.

  FIG. 7 shows an embodiment of the image forming apparatus according to the twelfth aspect. This image forming apparatus is an optical printer, and has a photoconductive photosensitive member 111 formed in a cylindrical shape as a photosensitive medium that forms the surface to be scanned, and a charging means 112 (contact type by a charging roller) around the photosensitive member. A corona charger or a charging brush can be used), a developing device 113, a transfer means 114 (a transfer roller is shown, but a corona charger may be used), and a cleaning device 115. Have. Reference numeral 116 denotes a fixing device.

  Further, an optical scanning device 117 is provided, and image writing by optical scanning is performed between the charging unit 112 and the developing device 113. As the optical scanning device, the laser scanning device of Example 1 described above can be used.

  When image formation is performed, the photosensitive member 111 is rotated at a constant speed in the direction of the arrow, the surface thereof is uniformly charged by the charging unit 112, and then an image is written by optical scanning by the optical scanning device 117, corresponding to the written image. An electrostatic latent image is formed. The formed electrostatic latent image is a so-called “negative latent image” and the image portion is exposed.

  The electrostatic latent image is reversely developed by the developing device 113 and visualized as a toner image. The toner image is transferred by a transfer unit 114 onto a sheet-like recording medium S such as transfer paper or an OHP sheet, and is fixed by a fixing device 116. The sheet-like recording medium S on which the toner image is fixed is discharged out of the apparatus, and the photoreceptor 111 after the toner image is transferred is cleaned by a cleaning device 115 to remove residual toner and paper dust.

  The optical scanning device can be made into a multi-beam, the polygon rotation speed can be reduced, and the power consumption can be reduced. Of course, a plurality of “toner images having different colors” can be formed by using a plurality of laser scanning devices and a plurality of photoconductors, and these can be superimposed to form a color image.

It is a figure for demonstrating an example of the optical arrangement | positioning of a laser scanning apparatus. It is a figure for demonstrating the space | interval of each lens in the optical arrangement | positioning of FIG. It is a figure which shows explanatoryally the diffraction surface in Example 1. FIG. It is a figure for demonstrating the characterizing part of Claims 9 and 10. It is a figure for demonstrating the cross-sectional shape of a diffraction surface. It is a figure for demonstrating the effect which makes the entrance side of a 1st lens into a curved surface. It is a figure for demonstrating one Embodiment of an image forming apparatus.

Explanation of symbols

1 Semiconductor laser 2 Coupling lens
4 First lens 5 Polygon mirror 6, 7 Scanning optical system 8 Dustproof glass 9 Scanned surface 10 Soundproof glass

Claims (12)

A semiconductor laser;
A coupling optical system for coupling a light beam from the semiconductor laser;
A first optical system for guiding a light beam from the coupling optical system to an optical deflector;
An optical deflector for deflecting the laser beam from the first optical system in the main scanning direction;
A laser scanning device provided with a scanning optical system for condensing the laser beam deflected by the optical deflector toward the surface to be scanned,
The coupling optical system has a diffractive surface having the same power in the main scanning direction and the sub-scanning direction,
The first optical system has a diffractive surface having power only in the sub-scanning direction. The laser scanning device according to claim 1.
A laser scanning device, wherein the coupling optical system emits substantially parallel light. The laser scanning device according to claim 1 or 2,
A laser scanning device, wherein the coupling optical system has a refractive surface having a positive power. The laser scanning device according to claim 1, 2 or 3,
A laser scanning device, wherein the coupling optical system includes a resin lens having a diffractive surface having a positive power. The laser scanning device according to any one of claims 1 to 4,
The laser scanning device, wherein the first optical system includes a resin lens having a diffractive surface having a positive power in the sub-scanning direction. The laser scanning device according to any one of claims 1 to 5,
A laser scanning device, wherein the first optical system has a refractive surface having negative power in the sub-scanning direction. A semiconductor laser;
A coupling optical system for coupling the laser beam from this light source;
A first optical system for guiding a laser beam from the coupling optical system to an optical deflector;
An optical deflector for deflecting the laser beam from the first optical system in the main scanning direction;
A laser scanning device provided with a scanning optical system for condensing the laser beam deflected by the optical deflector toward the surface to be scanned,
A laser scanning device, wherein the lens constituting the first optical system has a diffractive surface having power only in the sub-scanning direction and a refracting surface having negative power in the sub-scanning direction. The laser scanning device according to any one of claims 1 to 7,
A first holding member for holding the semiconductor laser and the coupling optical system;
The laser scanning device, wherein the coupling optical system is fixed to the first holding member after the position is adjusted at least in the optical axis direction. The laser scanning device according to claim 8.
A second holding member that holds at least the first holding member and the first optical system;
The laser scanning device, wherein after the coupling optical system is fixed to the first holding member, the first optical system is fixed to the second holding member after being adjusted at least in the optical axis direction. The laser scanning device according to any one of claims 1 to 9,
The diffractive surface of the coupling optical system is rotationally symmetric with respect to the optical axis,
The diffractive surface of the first optical system is a diffractive surface in which gratings are arranged in the sub-scanning direction. In the laser scanning device according to any one of claims 1 to 10,
A laser scanning device, wherein the scanning optical system includes at least one resin lens. An image forming apparatus using the laser scanning device according to any one of claims 1 to 11.

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