CN201477287U - Short-focusing-distance two-piece type f theta lens - Google Patents

Abstract

A short-focusing-distance two-piece type f theta lens is used for a laser scanning device with a rotary polygonal mirror, wherein a first lens is provided with a first optical surface and a second optical surface, and a second lens is provided with a third optical surface and a fourth optical surface; the two-piece type f theta lens is characterized in that each optical surface of the two-piece type f theta lens is an aspheric surface in the main scanning direction; in the main scanning direction on the optical axis, the concave surfaces of the first, second and third optical surfaces are on the side of the rotary polygonal mirror, the fourth optical surface has an inflection point and the convex surface is on the side of the rotary polygonal mirror; and optical conditions are satisfied: 0.5429 is less than or equal to tan (beta) is less than or equal to 1.2799; where β is the maximum effective window angle. The first lens and the second lens of the short-focusing-distance two-piece type f theta lens are arranged, so that the distance from the rotary polygonal mirror to an imaging surface can be effectively shortened, and the specific purpose of reducing the volume of the laser scanning device is achieved.

Description

Two-piece fθ lens with short focusing distance

technical field

The utility model relates to a short focusing distance two-piece fθ lens of a laser scanning device, in particular to a laser scanning unit (Laser scanning unit) for a rotating polygon mirror (Polygon mirror), which has a short focusing distance to reduce Two-piece fθ lens for laser scanning device volume.

Background technique

At present, the laser scanning device (LSU: Laser Scanning Unit) used by the laser printer (LBP: Laser Beam Print) uses a high-speed rotating polygon mirror (polygon mirror) to control the scanning action of the laser beam (laser beam scanning), as shown in the US Patent US7,079,171, US6,377,293, US6,295,116, or as described in Taiwan Patent I198966. The principle is briefly described as follows: use a semiconductor laser to emit a laser beam, first pass through a collimator, and then pass through an aperture to form a parallel beam, and then the parallel beam passes through a cylindrical lens (cylindrical lens) , the width on the X-axis in the sub-scanning direction (sub scanning direction) can be focused parallel to the Y-axis in the main scanning direction (main scanning direction) to form a line image (lineimage), and then projected to the high-speed rotation On the polygon mirror, the rotating polygon mirror is evenly and continuously provided with a reflection mirror, which is just at or close to the focus position of the above-mentioned line image. The projection direction of the laser beam is controlled by rotating the polygon mirror. When the multiple mirrors arranged continuously on the rotating polygon mirror are rotating at high speed, the laser beam incident on one of the mirrors can be directed along the direction of the main scanning direction (Y axis). The parallel direction is deflected and reflected to the fθ linear scanning lens at the same angular velocity, and the fθ linear scanning lens is arranged beside the rotating polygonal mirror, which can be a single-element scanning lens or two One-piece lens construction. The function of this fθ linear scanning lens is to focus the laser beam that is reflected by the reflector on the polygon mirror and enter the fθ lens into a circular (or elliptical) light spot and project it on the light receiving surface (photoreceptor drum, ie On the imaging plane), and meet the requirements of linear scanning (scanning linearity), such as US patents US4,707,085, US6,757,088; Japanese patent JP2004-294713, etc. However, the existing fθ linear scanning lenses have the following problems:

(1) When the rotating polygonal mirror reflects the laser beam, the central axis of the laser beam projected on the rotating polygonal mirror is not directly facing the central axis of rotation of the rotating polygonal mirror, so that when designing the fθ linear scanning mirror, it is necessary to consider the rotation of the polygonal mirror at the same time Mirror off-axis deviation (reflection deviation) problem; in the prior art, the optical correction in the sub-scanning direction is used to correct the optical correction in the main scanning direction, such as US Pat. . However, in order to properly correct the off-axis deviation through the sub-scanning direction, a longer focal length is required, which also increases the volume of the laser scanning device.

(2), in order to make the diameter of the light spot of the scanning light of the fθ linear scanning lens on the photosensitive drum meet the requirements of the use specification, in the prior art, a longer focal length is often used to make the image quality better, and even a reflector is used Extend the imaging distance, such as US2002/0063939; or use three-piece lenses such as US2002/0030158, US5,086,350, Japanese patent JP63-172217; Patents US2001/0009470, US5,838,480, etc.; or use a two-piece lens with an inflection point, such as US patents US5,111,219, US7,057,781, US6,919,993; or use a single piece with an inflection point Type lens, such as Japanese patent JP04-50908.

(3), for the use of small printers, in order to reduce the volume of the laser scanning device LSU, one of the methods is to shorten the imaging distance on the photosensitive drum, such as U.S. Patent No. 7,130,096, etc., to limit the effective scanning range ) to the ratio of the imaging optical distance (optical length) to shorten the imaging distance on the photosensitive drum and eliminate the ghost image (ghost image); US Pat. , Focal Distance) and the focal length ratio (d/f) of the fθ lens to shorten the distance, but taking the focal length as 100mm as an example, the focusing distance is about 200mm; scanning line) to the optical surface of the fθ lens, but its maximum scanning angle is about 27.6 degrees, which is not enough to effectively reduce the focusing distance.

In order to meet consumers' demand for light, thin and small laser scanning devices, for short focusing distance (for example, for A4 laser printers, the focusing distance is less than 150mm) and in the main scanning and sub-scanning directions, it can effectively correct optical distortion, improve scanning quality and It is an urgent need for users to increase the resolution.

Utility model content

The purpose of this utility model is to provide a short focusing distance two-piece fθ lens of a laser scanning device, which is suitable for a laser scanning device with a rotating polygon mirror. The two-piece fθ lens is counted sequentially from the rotating polygon mirror, wherein The first lens has a first optical surface and a second optical surface, and the second lens has a third optical surface and a fourth optical surface; it is characterized in that each optical surface of the two-piece fθ lens is an aspheric surface in the main scanning direction; In the main scanning direction of the optical axis, the concave surfaces of the first, second and third optical surfaces are on the side of the rotating polygon mirror, and the fourth optical surface has an inflection point and its convex surface is on the side of the rotating polygon mirror; it is mainly used to uniformize the scanning light on the side of the rotating polygon mirror. In the main scanning direction and the sub-scanning direction, the imaging deviation is formed on the photosensitive drum due to the offset of the optical axis, and the scanning light is corrected and focused on the target; the scanning light reflected by the rotating polygon mirror can be corrected on the target Imaging, to achieve the linear scanning effect required by the laser scanning device.

Another object of the present invention is to provide a short focusing distance two-piece fθ lens of a laser scanning device. Since the fθ lens has a short focusing distance, the volume of the laser scanning device can be reduced and the imaging effect is good, and Satisfy 0.5429≤tan(β)≤1.2799, where β is the maximum effective window angle (maximum angle of effective window), that is, between 28.5° and 52°. The laser beam reflected by the rotating polygonal mirror passes through the two-piece fθ lens with a short focusing distance, so that the scanning light can still meet the requirements of the spot area projected on the target object at a short focusing distance, achieving reduction The effect of laser scanning device volume.

Another object of the present utility model is to provide a short focusing distance two-piece fθ lens of a laser scanning device, which can correct distortion due to the deviation of the scanning light from the optical axis, resulting in an increase in the offset in the main scanning direction and the sub-scanning direction. It solves the problem of distorting the light spots formed on the photosensitive drum, and makes the size of each imaging light spot uniform, so as to achieve the effect of improving the resolution quality.

Therefore, the short focusing distance two-piece fθ lens of the laser scanning device of the present invention is suitable for at least including a rotating polygon mirror, and the laser beam emitted by the light source is reflected into scanning light by the reflector arranged on the rotating polygon mirror. Imaging on the target object; for laser printers, the target object is often a photosensitive drum (drum), that is, the light spot to be imaged emits a laser beam through the light source, and scans through the mirror of the rotating polygonal mirror to form scanning light, which scans the light After correcting the angle and position of the two-piece fθ lens of the utility model, a light spot (spot) is formed on the photosensitive drum. Since the photosensitive drum is coated with a photosensitizer, it can sense the toner and make it gather on the paper, so that the data can be print out.

Description of drawings

Fig. 1 is the optical path schematic diagram of the utility model short focusing distance two-piece fθ lens;

Fig. 2 is the schematic diagram that the scanning light of the utility model's short focusing distance two-piece fθ lens passes through the optical path, symbol and light spot area of the first lens and the second lens as the projection positions vary;

Fig. 3 is a schematic diagram of the fourth optical surface inflection point of the second lens of the utility model with a short focusing distance of two fθ lenses;

Fig. 4 is an explanatory diagram of geometric light spots and symbols projected on the photosensitive drum by the scanning light through the two-piece fθ lens with short focusing distance of the present invention;

Fig. 5 is a schematic diagram of the maximum angle of the effective window of the two-piece fθ lens with a short focusing distance of the utility model and the photosensitive drum;

Fig. 6 is the optical path diagram of the first embodiment of the utility model;

Fig. 7 is a light point distribution diagram on the photosensitive drum according to the first embodiment;

Fig. 8 is a light spot size and shape diagram at different positions on the target according to the first embodiment;

Fig. 9 is the optical path diagram of the second embodiment;

Fig. 10 is a light point distribution diagram on the photosensitive drum according to the second embodiment;

Fig. 11 is a light spot size and shape diagram at different positions on the target according to the second embodiment;

Fig. 12 is the optical path diagram of the third embodiment;

Fig. 13 is a light point distribution diagram on a photosensitive drum according to a third embodiment;

Fig. 14 is a light spot size and shape diagram at different positions on the target according to the third embodiment;

Fig. 15 is the optical path diagram of the fourth embodiment;

Fig. 16 is a light point distribution diagram on a photosensitive drum according to a fourth embodiment;

Fig. 17 is a light spot size and shape diagram at different positions on the target according to the fourth embodiment;

Fig. 18 is the optical path diagram of the fifth embodiment;

Fig. 19 is a light point distribution diagram on a photosensitive drum according to a fifth embodiment;

Fig. 20 is a diagram of the size and shape of light spots at different positions on the target according to the fifth embodiment;

Fig. 21 is the optical path diagram of the sixth embodiment;

Fig. 22 is a light spot distribution diagram on the photosensitive drum according to the sixth embodiment;

Fig. 23 is a diagram showing the size and shape of light spots at different positions on the target according to the sixth embodiment.

表示光点X方向均方根大小，

表示光点Y方向均方根大小，

表示光点最大半径；图8、11、14、17、20、23中，D表示直径＝100μm。Wherein, in Fig. 7, 10, 13, 16, 19, 22, the horizontal axis represents the distance from the optical axis, and the vertical axis represents the spot size,

Indicates the root mean square size of the light point in the X direction,

Indicates the root mean square size of the light point in the Y direction,

Indicates the maximum radius of the light spot; in Figures 8, 11, 14, 17, 20, and 23, D indicates diameter = 100 μm.

[Description of main component symbols]

10: rotating polygonal mirror; 11: laser light source;

111: light beam; 113a, 113b, 113c: scanning light;

131: the first lens; 131a: the first optical surface;

131b: the second optical surface; 132: the second lens;

132a: the third optical surface; 132b: the fourth optical surface;

15: Photosensitive drum; 16: Cylindrical mirror;

2, 2a, 2b, 2c: light spot; 3: effective scanning window.

Detailed ways

Fig. 1 is a schematic diagram of the optical path of the short focusing distance two-piece fθ lens of the laser scanning device of the present invention. As shown in the figure, the short focusing distance two-piece fθ lens of the laser scanning device of the present invention includes a first lens 131 having a first optical surface 131a and a second optical surface 131b, and a third optical surface 132a and a fourth optical surface 131b. The second lens 132 on the optical surface 132b is suitable for a laser scanning device. In the figure, the laser scanning device mainly includes a laser light source 11, a rotating polygonal mirror 10, a cylindrical mirror 16 and a photosensitive target. In the figure, the target is implemented with a photosensitive drum (drum) 15. The beam 111 generated by the laser light source 11 passes through the cylindrical mirror 16 and is projected onto the rotating polygon mirror 10 . The rotating polygonal mirror 10 has reflective mirrors (five-sided reflective mirrors in the figure), and the reflective mirrors rotate around the central axis to reflect the light beam 111 into scanning rays 113a, 113b, 113c. Wherein the projection of the scanning rays 113a, 113b, 113c in the X direction is called the sub scanning direction (sub scanning direction), the projection in the Y direction is called the main scanning direction (main scanning direction), and the scanning angle of the rotating polygon mirror 10 is θ, scanning rays 113a, 113b, 113c form the distance between the left end (left end) and the right end (right end) on the photosensitive drum 15 after being emitted from the fourth optical surface 132b of the fθ lens, which is the effective window 3 (effective window) distance, As shown in Figure 2, the light spots within the effective window distance can print the original file data into drawings.

Referring to FIG. 1 and FIG. 2 , FIG. 2 is an optical path diagram of the scanning light passing through the first lens and the second lens. When the laser light source 11 starts to emit the laser beam 111, it is reflected as scanning light through the rotating polygon mirror 10, and when the scanning light passes through the first mirror 131, it is refracted by the first optical surface 131a and the second optical surface 131b of the first mirror 131, and the The scanning light whose distance and time are reflected by the rotating polygon mirror 10 is converted into the scanning light whose distance and time are linear. When the scanning light passes through the first lens 131 and the second lens 132, due to the optical properties of the first optical surface 131a, the second optical surface 131b, the third optical surface 132a, and the fourth optical surface 132b, the scanning light is focused on the photosensitive drum 15, and form a row of light spots (Spot) 2 on the photosensitive drum 15. Wherein, d0 (not shown) is the minimum distance of cylindrical mirror 16 along the optical surface of rotating polygonal mirror 10 to the reflector of rotating polygonal mirror 10 along the laser beam center, and _d1 is the distance from rotating polygonal mirror 10 to the first optical surface 131a pitch, _d2 is the distance from the first optical surface 131a to the second optical surface 131b, _d3 is the distance from the second optical surface 131b to the third optical surface 132a, _d4 is the distance from the third optical surface 132a to the fourth optical surface 132b d5 is the distance from the fourth optical surface 132b to the photosensitive drum 15, R1 is the radius of curvature of the first optical surface 131a (Curvature), R2 is the radius of curvature of the second optical surface 131b, R3 is the radius of the third optical surface 132a The curvature radius, R4 is the curvature radius of the 4th optical surface 132b.

The fourth optical surface 132b is an optical surface with an inflection point in the main scanning direction. As shown in FIG. Rotate the polygon mirror 10 sides. FIG. 4 is a schematic diagram of the spot area changing with different projection positions after the scanning light is projected on the photosensitive drum. When the scanning light 113a passes through the first lens 131 and the second lens 132 along the optical axis and is projected on the photosensitive drum 15, because the incident angle on the first lens 131 and the second lens 132 is zero, the main scanning direction produces The deviation rate is the smallest, so the light spot 2a imaged on the photosensitive drum 15 is a quasi-circle. When the scanning light rays 113b and 113c pass through the first lens 131 and the second lens 132 and project on the photosensitive drum 15, the angle formed by the first lens 131 and the second lens 132 with the optical axis is not zero. , so that the offset rate generated in the main scanning direction is larger than the optical axis, and the projection length in the main scanning direction is larger than the light spot formed by the scanning light 113a; this situation is also the same in the sub-scanning direction, so the deviation The light spot formed by the scanning light of the optical axis will also be larger; therefore, the light spot 2b, 2c imaged on the photosensitive drum 15 is similar to an ellipse, and the area of 2b, 2c is larger than 2a. Wherein, S _a0 and S _b0 are the root mean square radii (Rootmeans square of spot size radius on mirror) of the spot of the scanning light on the main scanning direction (Y direction) and sub-scanning direction (X direction) on the reflection surface of the rotating polygon mirror 10 ), S _a and S _b are the root mean square radii (Root means square of spot size radius on target) of the spot size on the target object in the X direction and the Y direction, respectively.

FIG. 5 is a schematic diagram of the effective window and the maximum effective window angle (beta) of the scanning light projected on the photosensitive drum. After the leftmost scanning light 113c exits the fourth optical surface 132b of the second lens 132, the angle between the scanning light and a straight line parallel to the optical axis is the maximum value of the effective window angle; usually, the rightmost scanning light 113b and the leftmost The scanning light 113c is symmetrical. In order to reduce the volume of the laser scanning device, the imaging distance from the rotating polygon mirror 10 to the photosensitive drum 15 is shortened, that is, the focusing distance is shortened. In order to shorten the focusing distance, in addition to the optical properties of the four optical surfaces of the first lens 131 and the second lens 132, the materials used (refractive index, Abbe number) of the first lens 131 and the second lens 132, etc. Designed to shorten the focusing distance (d1+d2+d3+d4+d5), especially the air gap (d1+d3+d5), it can also increase the value of the maximum effective window angle β to make the opening angle of the scan Increase, the relationship between the maximum effective window angle β and the distance from the second lens 132 to the photosensitive drum 15 is shown in formula (1). When the value of β is increased, the value of y _a can be effectively shortened under a fixed effective window.

$\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; the\; tan</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}}{{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Wherein, y _a is the distance from the optical axis to the imaging surface of the photosensitive drum 15 that is flat on the fourth optical surface 132b of the second lens 132 and is emitted from the endmost scanning ray (the leftmost end 113c or the rightmost end 113b) in the main scanning direction (Y direction); y _b is the distance from the endmost scanning light (leftmost end 113c or rightmost end 113b ) in the main scanning direction (Y direction) emitted from the fourth optical surface 132b of the second lens 132 to the imaging surface of the photosensitive drum 15 .

In summary, the two-piece fθ lens with a short focusing distance of the present invention can correct the scanning light reflected by the rotating polygon mirror 10, correct the scanning light of the Gaussian beam for distortion, and convert the relationship between time and angular velocity In the main scanning direction and sub-scanning direction, the beam radii of the scanning light in the X direction and Y direction pass through the angles of the fθ lens to generate uniform light spots on the imaging surface to provide resolution that meets the requirements ; and can effectively shorten the focusing distance to reduce the volume of the laser scanning device.

In order to achieve the above-mentioned effects, the utility model has a short focusing distance two-piece fθ lens on the first optical surface 131a or the second optical surface 132a of the first lens 131 and the third optical surface 132a or the fourth optical surface of the second lens 132 132b. In the main scanning direction or the sub-scanning direction, a spherical surface or an aspheric surface design can be used. If an aspheric surface design is used, the aspheric surface satisfies the following surface equation:

1: Torical equation

$\mathrm{<span\; class="notranslate">\; Z</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; Zy</span>}<span\; class="notranslate">\; +</span>\frac{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; Cxy</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\sqrt{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; Cxy</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}$

$\mathrm{<span\; class="notranslate">\; Cxy</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; Cx</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; Zy</span>}}$

$\mathrm{<span\; class="notranslate">\; Zy</span>}<span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; Cy</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; Y</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\sqrt{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; Ky</span>}<span\; class="notranslate">\; )</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; Cy</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; Y</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; Y</span>}}^{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; 6</span>}}{\mathrm{<span\; class="notranslate">\; Y</span>}}^{\mathrm{<span\; class="notranslate">\; 6</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}}{\mathrm{<span\; class="notranslate">\; Y</span>}}^{\mathrm{<span\; class="notranslate">\; 8</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; 10</span>}}{\mathrm{<span\; class="notranslate">\; Y</span>}}^{\mathrm{<span\; class="notranslate">\; 10</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Among them, Z is the distance from any point on the lens in the direction of the optical axis to the tangent plane of the origin (SAG); C _y and C _x are the curvatures in the Y direction and X direction respectively; _Ky is the conic coefficient in the Y direction (Coniccoefficient) ; B ₄ , B ₆ , B ₈ and B ₁₀ are coefficients of the 4th, 6th, 8th, and 10th powers (4th～10thorder coefficients deformation from the conic); when C _x ＝C _y and K _y ＝A _P When =B _p =C _p =D _p =0, it is simplified to a single spherical surface.

2: Extended polynomial equation (Extended polynomial equation)

$\mathrm{<span\; class="notranslate">\; Z</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; CR</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\sqrt{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; C</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}<span\; class="notranslate">\; +</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; Y</span>}<span\; class="notranslate">\; )</span>$

$<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; CR</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\sqrt{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; C</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 11</span>}}\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 12</span>}}\mathrm{<span\; class="notranslate">\; Y</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; one</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; two</span>}}\mathrm{<span\; class="notranslate">\; X\; Y</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; three</span>}}{\mathrm{<span\; class="notranslate">\; Y</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}$

$<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 31</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 32</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; Y</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 33</span>}}{\mathrm{<span\; class="notranslate">\; X\; Y</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 34</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="Y"\; filenames="H2009201467186E00021.png"\; state="\{\{state\}\}">Y</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}$

$<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 41</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 42</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}\mathrm{<span\; class="notranslate">\; Y</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 43</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; Y</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 44</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="XY"\; filenames="H2009201467186E00021.png"\; state="\{\{state\}\}">X\; Y</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 45</span>}}{\mathrm{<span\; class="notranslate">\; Y</span>}}^{\mathrm{<span\; class="notranslate">\; 4</span>}}$

$<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 51</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 52</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 4</span>}}\mathrm{<span\; class="notranslate">\; Y</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 53</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; Y</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 54</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="Y"\; filenames="H2009201467186E00021.png"\; state="\{\{state\}\}">Y</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 55</span>}}{\mathrm{<span\; class="notranslate">\; X\; Y</span>}}^{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 56</span>}}{\mathrm{<span\; class="notranslate">\; Y</span>}}^{\mathrm{<span\; class="notranslate">\; 5</span>}}$

$<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 61</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 6</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 62</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 5</span>}}\mathrm{<span\; class="notranslate">\; Y</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 63</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; Y</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 64</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="Y"\; filenames="H2009201467186E00021.png"\; state="\{\{state\}\}">Y</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 65</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; Y</span>}}^{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 66</span>}}{\mathrm{<span\; class="notranslate">\; X\; Y</span>}}^{\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 67</span>}}{\mathrm{<span\; class="notranslate">\; Y</span>}}^{\mathrm{<span\; class="notranslate">\; 6</span>}}$

$<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 71</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 7</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 72</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 6</span>}}\mathrm{<span\; class="notranslate">\; Y</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 73</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 5</span>}}{\mathrm{<span\; class="notranslate">\; Y</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 74</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="Y"\; filenames="H2009201467186E00021.png"\; state="\{\{state\}\}">Y</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 75</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; Y</span>}}^{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 76</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; Y</span>}}^{\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 77</span>}}{\mathrm{<span\; class="notranslate">\; X\; Y</span>}}^{\mathrm{<span\; class="notranslate">\; 6</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 78</span>}}{\mathrm{<span\; class="notranslate">\; Y</span>}}^{\mathrm{<span\; class="notranslate">\; 7</span>}}$

$<span\; class="notranslate">\; +</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

Among them, Z is the distance from any point on the lens to the tangent plane of the origin in the direction of the optical axis (SAG); C is the curvature at the pole of the surface; K is the conic coefficient; A _ij is the ith power polynomial coefficients of .

In order to enable the scanning light to maintain equal scanning speeds on the imaging surface of the target object, for example, in two identical time intervals, the distance between the two light spots is maintained to be equal. The formula fθ lens can correct the scanning light emission angle between the scanning light 113c and the scanning light 113b through the first lens 131 and the second lens 132, so that the two scanning light at the same time interval, through the emission angle After the correction, the distances between the two light spots formed on the photosensitive drum 15 of the image are equal, that is, the size of the light spot imaged on the photosensitive drum 15 is uniform (limited to the range that meets the resolution requirements), so as to obtain the best Analysis effect.

The short focusing distance two-piece fθ lens of the present invention includes, counting from the rotating polygonal mirror 10, a first lens 131 and a second lens 132; wherein the first lens 131 has a first optical surface 131a and a second optical surface 131b , the second lens 132 has a third optical surface 132a and a fourth optical surface 132b; in the main scanning direction of the optical axis, the concave surfaces of the first, second, and third optical surfaces (131a, 131b, 132a) are on the rotating polygonal mirror 10 side , the fourth optical surface 132b has an inflection point and its convex surface is on the side of the rotating polygon mirror 10; it is the scanning light spot that the angle and time reflected by the rotating polygon mirror 10 are in a nonlinear relationship and converted into a scanning that is a linear relationship in distance and time The light spot is focused on the target object after correcting the optical distortion; wherein, the first optical surface 131a, the second optical surface 131b, the third optical surface 132a and the fourth optical surface 132b are all aspherical in the main scanning direction Composed of optical surfaces; the first optical surface 131a, the second optical surface 131b, the third optical surface 132a, and the fourth optical surface 132b may have at least one optical surface composed of an aspherical surface in the sub-scanning direction. Furthermore, in terms of the composition of the first lens 131 and the second lens 132, and in terms of optical effects, the two-piece fθ lens of the present utility model further satisfies the formula (4)～Formula (5) conditions:

$\mathrm{<span\; class="notranslate">\; 2.5</span>}<span\; class="notranslate">\; \&le;</span>\frac{{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="d"\; filenames="H2009201467186E00021.png"\; state="\{\{state\}\}">d</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; 5.2</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

0.5429≤tan(β)≤1.2799 (5)

Or, satisfy formula (6) in the main scanning direction

$\mathrm{<span\; class="notranslate">\; 0.06</span>}<span\; class="notranslate">\; \&le;</span><span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; (</span>\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}}}<span\; class="notranslate">\; +</span>\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span><span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; 0.22</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

Wherein, _d1 is the distance from the reflective surface of the rotating polygon mirror 10 on the optical axis to the optical surface of the first mirror 131 on the side of the rotating polygon mirror, and _d3 is the distance from the optical surface of the first mirror 131 on the object side of the first mirror 131 to the rotating polygon of the second mirror 132 on the optical axis The distance of the optical surface on the mirror 10 side, _d5 is the distance from the second lens 132 target side optical surface on the optical axis to the target object, f _s is the composite focal length of the two-piece fθ lens, β is the maximum effective window angle, f _{(1) Y} is the focal length of the first mirror 131 in the main scanning direction, f _{(2) Y} is the focal length of the second mirror 132 in the main scanning direction, n _d1 and n _d2 are the refractions of the first mirror 131 and the second mirror 132 rate (refraction index).

Furthermore, the uniformity of the light spot formed by the short focusing distance two-piece fθ lens of the present utility model can be expressed by the ratio of the maximum radius _Smax of the light spot at the Y position of the scanning light on the photosensitive drum 15, that is, Satisfy formula (7):

$\mathrm{<span\; class="notranslate">\; 0.10</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; \&delta;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; min</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; Y</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; max</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; Y</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

Among them, δ is the ratio of the smallest light spot to the largest light spot on the target.

Furthermore, the resolution formed by the two-piece fθ mirror of the present utility model can use η _max to be the geometric spot (geometric spot) of the scanning light on the reflective surface of the rotating polygon mirror 10 through scanning the geometric spot on the photosensitive drum 15 The ratio of the maximum value and η _min represent by scanning the ratio of the geometric light point minimum value on the photosensitive drum 15 through scanning the geometric light spot of the scanning light on the rotating polygonal mirror 10 reflective surfaces, which can satisfy formula (8) and (9),

${\mathrm{<span\; class="notranslate">\; \&eta;</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; max</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; )</span>}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="0"\; label="S\; b"\; filenames="H2009201467186E00081.png,H2009201467186E00171.png"\; state="\{\{state\}\}">S</figure-callout></span><figure-callout\; id="0"\; label="S\; b"\; filenames="H2009201467186E00081.png,H2009201467186E00171.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; </span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; 0.05</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; \&eta;</span>}}_{\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; min</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; )</span>}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="0"\; label="S\; b"\; filenames="H2009201467186E00081.png,H2009201467186E00171.png"\; state="\{\{state\}\}">S</figure-callout></span><figure-callout\; id="0"\; label="S\; b"\; filenames="H2009201467186E00081.png,H2009201467186E00171.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; </span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; 0.005</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 9</span>}<span\; class="notranslate">\; )</span>$

Wherein, S _a and S _b are the root-mean-square radius of any light spot formed by scanning light on the photosensitive drum 15 in the X direction and the Y direction, δ is the ratio of the minimum light spot to the maximum light spot on the photosensitive drum 15, and η is S _a0 and S _b0 are the average ratio of the light spot of the scanning light on the reflection surface of the rotating polygon mirror 10 in the sub-scanning direction and the main scanning direction. Square root radius.

In order to make the utility model more definite and detailed, the preferred embodiments are listed hereby and cooperate with following illustrations, the structure of the utility model and its technical characteristics are described in detail as follows:

The following embodiments of the present invention are described for the main components of the two-piece fθ lens of the rotating polygonal mirror laser scanning device of the present invention. Therefore, the following embodiments of the present invention are applied to In the rotating polygonal mirror laser scanning device, as far as the general laser scanning device is concerned, except for the two-piece fθ mirror disclosed by the utility model, other structures belong to the general known technology, so those who are generally familiar with this technology in this field Personnel understand that the components of the two-piece fθ lens of the rotating polygon mirror laser scanning device disclosed in the present invention are not limited to the embodiment structures disclosed below, that is, the two-piece fθ lens of the rotating polygon mirror laser scanning device Various components of the lens can be changed, modified, or even equivalently changed. For example, the design of the radius of curvature, material selection, and distance adjustment of the first lens 131 and the second lens 132 are not limited. And for the convenience of description and comparison, the following embodiments all use the light spots S _a0 =7.22 (μm) and S _b0 =660.94 (μm) on the rotating polygon mirror 10 , but not limited thereto.

<First embodiment>

The second optical surface 131b of the first lens 131 and the third optical surface 132a of the second lens 132 of the short focusing distance two-piece fθ lens of this embodiment are both aspherical surfaces, and the formula (3) is used as the aspheric surface formula Design the curved surface of its optical surface; the main scanning direction of the first optical surface 131a of the first eyeglass 131, the 4th optical surface 132b of the second eyeglass 132 is aspheric surface, use formula (2) to design its optics for aspheric surface formula surface of the face. Its optical characteristics and aspheric surface parameters are shown in Table 1 and Table 2. The optical path diagram is shown in FIG. 6 , and the inflection point of the fourth optical surface 132b is located at ψ=4.12°.

Table 1. The fθ optical characteristics of the first embodiment

*Denotes aspherical

Table two (A), the optical surface aspherical parameters of the first embodiment

Table two (B) the optical surface aspherical parameters of the first embodiment

Through the optical surface of the two-piece fθ lens with short focusing distance, f _(1)Y = 118.315, f _(2)Y = 22389.4 (mm), y _a = 71.50, y _b = 53.47 (mm) , so that the maximum window angle β=37.01°, the light spot on the rotating polygon mirror 10 can be scanned to become a scanning ray, which can be focused on the photosensitive drum 15 to form a smaller light spot, and satisfy the formulas (4)-(6) and The conditions of formula (7)～(9), as table three; On the photosensitive drum 15, the geometric light spot diameter (μm) of the light spot with the central axis Z axis in the Y direction apart from the central axis Y distance (mm) is as table four ; And the light spot distribution diagram and the light spot size and shape diagram of the present embodiment are shown in FIG. 7 and FIG. 8 .

Table three, the first embodiment satisfies the condition table

Table 4. The maximum radius and root mean square radius of the light spot on the photosensitive drum of the first embodiment

<Second Embodiment>

The second optical surface 131b of the first lens 131 and the third optical surface 132a of the second lens 132 of the short focusing distance two-piece fθ lens of this embodiment are both aspherical surfaces, and the formula (3) is used as the aspheric surface formula Design the curved surface of its optical surface; The main scanning direction of the first optical surface 131a of the first eyeglass 131, the 4th optical surface 132b of the second eyeglass 132 is all aspheric surface, use formula (2) to design its aspheric surface formula The surface of the optical face. Its optical characteristics and aspheric surface parameters are shown in Table 5 and Table 6. The optical path diagram is shown in FIG. 9 , and the inflection point of the fourth optical surface 132b is located at ψ=6.47°.

Table five, fθ optical characteristics of the second embodiment

*Denotes aspherical

Table six (A), the optical surface aspheric parameters of the second embodiment

Table six (B) the optical surface aspherical parameters of the second embodiment

Through the optical surface of the short focusing distance two-piece type fθ lens formed here, f _(1)Y =89.253, f _(2)Y =-306.107(mm), and its y _a =79.73, y _b =55.15 (mm ), so that the maximum window angle β=34.673°, the light spot on the rotating polygon mirror 10 can be scanned into a scanning ray, which can be focused on the photosensitive drum 15 to form a smaller light spot, and satisfy the formulas (4)-(6) And the condition of formula (7)～(9), as table seven; On the photosensitive drum 15, the geometric light spot diameter (μm) of the light spot apart from the central axis Y distance (mm) with the central axis Z axis in the Y direction, as shown in the table Eight; and the light spot distribution diagram and the light spot size and shape diagram of this embodiment are shown in FIG. 10 and FIG. 11 .

Table seven, the second embodiment satisfies the condition table

Table 8. The maximum radius and root mean square radius of the light spot on the photosensitive drum of the second embodiment

<Third Embodiment>

The second optical surface 131b of the first lens 131 and the third optical surface 132a of the second lens 132 of the short focusing distance two-piece fθ lens of this embodiment are both aspherical surfaces, and the formula (3) is used as the aspheric surface formula Design the curved surface of its optical surface; The main scanning direction of the first optical surface 131a of the first eyeglass 131 and the 4th optical surface 132b of the second eyeglass 132 are all aspheric surfaces, use formula (2) to design its aspheric surface formula The surface of the optical face. Its optical properties and aspheric surface parameters are shown in Table 9 and Table 10. The optical path diagram is shown in Figure 12, and the inflection point of the fourth optical surface 132b is located at ψ=31.86°.

Table nine, fθ optical characteristics of the third embodiment

*Denotes aspherical

Table 10 (A), the aspherical parameters of the optical surface of the third embodiment

Table 10 (B) Optical surface aspherical parameters of the third embodiment

Through the optical surface of the two-piece fθ lens with short focusing distance, f _(1)Y =85.306, f _(2)Y =-281.708 (mm), and its y _a =79.34, y _b =88.70 (mm ), so that the maximum window angle β=48.188°, the light spot on the rotating polygon mirror 10 can be scanned into a scanning ray, which can be focused on the photosensitive drum 15 to form a smaller light spot, and satisfy the formulas (4)-(6) And the condition of formula (7)～(9), as table eleven; On the photosensitive drum 15, the geometric light spot diameter (μm) of the light spot apart from the central axis Y distance (mm) with the central axis Z axis in the Y direction, as Table 12; and the light spot distribution diagram and the light spot size and shape diagram of the present embodiment, as shown in FIG. 13 and FIG. 14 .

Table eleven, the third embodiment satisfies the condition table

Table 12. The maximum radius and root mean square radius of the luminous spot on the photosensitive drum of the third embodiment

<Fourth Embodiment>

The second optical surface 131b of the first lens 131 and the third optical surface 132a of the second lens 132 of the short focusing distance two-piece fθ lens of this embodiment are both aspherical surfaces, and the formula (3) is used as the aspheric surface formula Design the curved surface of its optical surface; The main scanning direction of the first optical surface 131a of the first eyeglass 131 and the 4th optical surface 132b of the second eyeglass 132 are all aspheric surfaces, use formula (2) to design its aspheric surface formula The surface of the optical face. Its optical properties and aspheric surface parameters are shown in Table 13 and Table 14. The optical path diagram is shown in FIG. 15 , and the inflection point of the fourth optical surface 132b is located at ψ=18.94°.

Table 13. The fθ optical characteristics of the fourth embodiment

*Denotes aspherical

Table 14 (A), the aspherical parameters of the optical surface of the fourth embodiment

Table 14 (B) Optical surface aspherical parameters of the fourth embodiment

Through the optical surface of the two-piece fθ lens with short focusing distance, f _(1)Y =89.817, f _(2)Y =-232.765 (mm), and its y _a =71.50, y _b =53.468 (mm ), so that the maximum window angle β=36.789°, the light spot on the rotating polygon mirror 10 can be scanned into a scanning ray, which can be focused on the photosensitive drum 15 to form a smaller light spot, and satisfy the formulas (4)-(6) And the condition of formula (7)～(9), as table fifteen; On the photosensitive drum 15, the geometric light spot diameter (μm) of the light spot apart from the central axis Y distance (mm) with the central axis Z axis in the Y direction, as Table 16; and the light spot distribution diagram and the light spot size and shape diagram of the present embodiment, as shown in Figure 16 and Figure 17.

Table 15, the fourth embodiment satisfies the condition table

Table 16. The maximum radius and root mean square radius of the light spot on the photosensitive drum of the fourth embodiment

<Fifth Embodiment>

The second optical surface 131b of the first lens 131 and the third optical surface 132a of the second lens 132 of the short focusing distance two-piece fθ lens of this embodiment are both aspherical surfaces, and the formula (3) is used as the aspheric surface formula Design the curved surface of its optical surface; The main scanning direction of the first optical surface 131a of the first eyeglass 131 and the 4th optical surface 132b of the second eyeglass 132 are all aspheric surfaces, use formula (2) to design its aspheric surface formula The surface of the optical face. Its optical characteristics and aspheric surface parameters are shown in Table 17 and Table 18. The optical path diagram is shown in Figure 18, and the inflection point of the fourth optical surface 132b is located at ψ=9.60°.

Table 17. The fθ optical characteristics of the fifth embodiment

*Denotes aspherical

Table 18 (A), the aspherical parameters of the optical surface of the fifth embodiment

Table 18 (B) Optical Surface Aspherical Parameters of the Fifth Embodiment

Through the optical surface of the two-piece fθ lens with short focusing distance, f _(1)Y =89.834, f _(2)Y =-314.630 (mm), and its y _a =72.694, y _b =48.158 (mm ), so that the maximum window angle β=33.523°, the light spot on the rotating polygon mirror 10 can be scanned into a scanning ray, which can be focused on the photosensitive drum 15 to form a smaller light spot, and satisfy the formulas (4)-(6) And the condition of formula (7)～(9), as table nineteen; On the photosensitive drum 15, the geometric light spot diameter (μm) of the light spot apart from the central axis Y distance (mm) with the central axis Z axis in the Y direction, as Table 20; and the light spot distribution diagram and the light spot size and shape diagram of the present embodiment, as shown in Figure 19 and Figure 20.

Table nineteen, the fifth embodiment satisfies the condition table

Table 20. The maximum radius and root mean square radius of the photosensitive drum on the photosensitive drum of the fifth embodiment

<Sixth Embodiment>

The second optical surface 131b of the first lens 131 and the third optical surface 132a of the second lens 132 of the short focusing distance two-piece fθ lens of this embodiment are both aspherical surfaces, and the formula (3) is used as the aspheric surface formula Design the curved surface of its optical surface; The main scanning direction of the first optical surface 131a of the first eyeglass 131 and the 4th optical surface 132b of the second eyeglass 132 are all aspheric surfaces, use formula (2) to design its aspheric surface formula The surface of the optical face. Its optical properties and aspheric surface parameters are shown in Table 21 and Table 22. The optical path diagram is shown in Figure 21, and the inflection point of the fourth optical surface 132b is located at ψ=13.07°.

Table 21. fθ optical characteristics of the sixth embodiment

*Denotes aspherical

Table 22 (A), the aspherical parameters of the optical surface of the sixth embodiment

Table 22 (B) Optical surface aspherical parameters of the sixth embodiment

Through the optical surface of the two-piece fθ lens with short focusing distance, f _(1)Y =89.991, f _(2)Y =-521.085 (mm), and its y _a =65.46, y _b =58.208 (mm ), so that the maximum window angle β=33.523°, the light spot on the rotating polygon mirror 10 can be scanned into a scanning ray, which can be focused on the photosensitive drum 15 to form a smaller light spot, and satisfy the formulas (4)-(6) And the condition of formula (7)～(9), as table twenty-three; On the photosensitive drum 15, the geometric light spot diameter (μm) of the light spot apart from the central axis Y distance (mm) with the central axis Z axis in the Y direction, See Table 24; and the light spot distribution diagram and light spot size and shape diagram of this embodiment are shown in Figure 22 and Figure 23.

Table 23, the sixth embodiment satisfies the condition table

Table 24. The maximum radius and root mean square radius of the light spot on the photosensitive drum of the sixth embodiment

Illustrate by above-mentioned embodiment, the utility model can reach following effect at least:

(1) Through the setting of the two-piece fθ lens of the utility model, the non-equal-rate scanning phenomenon of the rotating polygonal mirror on the imaging surface can be corrected to equal-velocity scanning, so that the projection of the laser beam on the imaging surface can be performed at an equal velocity. Scanning, so that the distance between two adjacent light spots formed on the target object is equal.

(2) Through the arrangement of the two-piece fθ lens of the utility model, the scanning light in the main scanning direction and the sub-scanning direction can be distorted and corrected, so that the light spot focused on the imaging target can be reduced.

(3) Through the arrangement of the two-piece fθ lens of the utility model, the scanning light in the main scanning direction and the sub-scanning direction can be distorted and corrected, so that the size of the light spot imaged on the target object can be uniformed.

(4) Through the arrangement of the two-piece fθ lens of the utility model, the focusing distance can be effectively shortened, the volume of the laser scanning device can be reduced, and the miniaturization requirement can be met.

The above is only a preferred embodiment of the utility model, and is only illustrative of the utility model, rather than restrictive; those skilled in the art understand that within the spirit and scope defined by the claims of the utility model, Many changes, modifications, and even equivalent changes are made to it, but all will fall within the protection scope of the present utility model.

Claims (4)

1. A short focusing distance two-piece fθ eyeglass, which is applicable to a laser scanning device, the laser scanning device at least includes a light source for emitting a laser beam, a rotating polygon mirror for reflecting the laser beam into scanning light, and a laser scanning device A light-sensitive target object; the short focusing distance two-piece fθ lens is counted sequentially from the rotating polygonal mirror, and is composed of a first lens and a second lens, and the first lens has a first optical surface and a second optical surface , the second lens has a third optical surface and a fourth optical surface, and it is characterized in that: the main scanning direction of the short focusing distance two-piece fθ lens on the optical axis, the first, second and third The concave surface of the optical surface is on the side of the rotating polygon mirror, the fourth optical surface has an inflection point and its convex surface is on the side of the rotating polygon mirror; the first optical surface, the second optical surface, the first optical surface The three optical surfaces and the fourth optical surface are all aspherical in the main scanning direction; and satisfy the following conditions: $\mathrm{<span\; class="notranslate">\; 2.5</span>}<span\; class="notranslate">\; \&le;</span>\frac{{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; 5.2</span>}<span\; class="notranslate">\; ;</span>$ 0.5429≤tan(β)≤1.2799; Wherein, _d1 is the distance from the rotating polygon mirror reflective surface on the optical axis to the rotating polygon mirror side optical surface of the first lens, and _d3 is the target object side optical surface of the first lens on the optical axis to the distance The distance between the rotating polygonal mirror side optical surface of the second lens, _d5 is the distance from the target object side optical surface of the second lens on the optical axis to the target object, and _fs is the distance of the two-piece fθ lens Compound focal length, β is the maximum effective window angle. 2. The two-piece fθ lens with short focusing distance according to claim 1, wherein the following conditions are further satisfied in the main scanning direction: $\mathrm{<span\; class="notranslate">\; 0.06</span>}<span\; class="notranslate">\; \&le;</span><span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; (</span>\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}}}<span\; class="notranslate">\; +</span>\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span><span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; 0.22</span>}<span\; class="notranslate">\; ;</span>$ Wherein, f _(1)Y is the focal length of the first lens in the main scanning direction, f _(2)Y is the focal length of the second lens in the main scanning direction, f _s is the composite focal length of the two-piece fθ lens, n _d1 and n _d2 are the refractive indices of the first lens and the second lens, respectively. 3. The short focusing distance two-piece fθ lens according to claim 1, characterized in that said scanning light forms a maximum light spot and a minimum light spot on said target, and said maximum light spot and said minimum light spot The size ratio satisfies: $\mathrm{<span\; class="notranslate">\; 0.10</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; \&delta;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; min</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; Y</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; max</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; Y</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ;</span>$ Wherein, S _{max, Y} is the maximum radius of the light spot at the Y position formed by the scanning light on the target, and δ is the ratio of the minimum light spot to the maximum light spot on the target. 4. The short focusing distance two-piece fθ lens according to claim 1, characterized in that the scanning light forms a maximum light spot and a minimum light spot on the target object, and the maximum light spot on the target object The ratio of the light spot to the ratio of the smallest light spot on the target satisfies respectively ${\mathrm{<span\; class="notranslate">\; \&eta;</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; max</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; )</span>}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; 0.05</span>}<span\; class="notranslate">\; ;</span>$ ${\mathrm{<span\; class="notranslate">\; \&eta;</span>}}_{\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; min</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; )</span>}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; 0.005</span>}$ Wherein, S _a0 and S _b0 are the root mean square radii of the light spot of the scanning light on the reflecting surface of the rotating polygon mirror in the sub-scanning direction and the main scanning direction, S _a and S _b are the The root-mean-square radius of any light spot formed by the scanning light in the sub-scanning direction and the main scanning direction, η _max , is the light spot of the scanning light on the target object after scanning on the reflecting surface of the rotating polygonal mirror. The ratio of the maximum light spot, _ηmin , is the ratio of the minimum light spot on the target by scanning the light spot of the scanning light on the reflective surface of the rotating polygon mirror.

Images