CN101650472B - Two-piece fθ mirror of MEMS laser scanning device - Google Patents

Abstract

A two-piece type f theta lens of a micro-electromechanical laser scanning device comprises a first lens and a second lens, wherein the first lens is a crescent lens with positive diopter and concave surface at the side of the micro-electromechanical reflector, the second lens is a crescent lens with negative diopter and convex surface at the side of the micro-electromechanical reflector, wherein the first lens has two optical surfaces, at least one of which is formed by aspheric surfaces in the main scanning direction, the second lens has two optical surfaces, at least one optical surface in the main scanning direction is formed by aspheric surface, which is mainly used to convert the scanning light beam whose angle reflected by the micro-electromechanical reflector and time are in nonlinear relation into the scanning light beam spot whose distance and time are in linear relation and correct the light beam spot on the target object, the first lens and the second lens both meet specific optical conditions to achieve the purposes of linear scanning effect and high resolution scanning.

Description

Two-piece fθ mirror of MEMS laser scanning device

technical field

The invention relates to a two-piece fθ lens of a micro-electromechanical laser scanning device, in particular to a micro-electromechanical mirror used to correct a simple harmonic motion to produce a sinusoidal angle change with time to achieve laser scanning The two-piece fθ lens for the linear scanning effect required by the device.

Background technique

At present, the laser scanning device LSU (Laser Scanning Unit) used in the laser beam printer LBP (Laser Beam Print) uses a high-speed rotating polygonal mirror to control the scanning action of the laser beam, such as US patent US7079171, US6377293, US6295116, or Taiwan patent I198966 described. The principle is briefly described as follows: the laser beam emitted by the semiconductor laser first passes through the collimating mirror, then passes through the aperture (aperture) to form a parallel beam, and after the parallel beam passes through the cylindrical mirror, it can be in the width of the sub-scanning direction (Y axis). It is parallel focused along the direction parallel to the main scanning direction (X-axis) to form a linear image, and then projected onto a high-speed rotating polygon mirror, and the polygon mirror is uniformly and continuously equipped with multiple mirrors, which are located at or close to The focus position of the above linear image. The projection direction of the laser beam is controlled by the polygon mirror. When a plurality of continuous mirrors rotate at high speed, the laser beam incident on a mirror can be deflected and reflected at the same angular speed along the direction parallel to the main scanning direction (X axis). to a fθ linear scanning mirror, and the fθ linear scanning mirror is arranged on one side of the polygon mirror, which may be a single-element scanning mirror or a two-element scanning mirror. The function of this fθ linear scanning mirror is to focus the laser beam that is reflected by the reflector of the polygon mirror and enter the fθ mirror into an elliptical light spot and project it on a light-receiving surface (ie, the imaging surface) to achieve linear scanning. Require. However, the traditional laser scanning device LSU has the following problems in use:

(1) The manufacture of the rotating polygonal mirror is difficult and expensive, which relatively increases the manufacture cost of the LSU.

(2) The polygonal mirror must have the function of high-speed rotation (such as 40,000 revolutions per minute), and the precision requirements are high, so that the Y-axis width of the reflective surface on the general polygonal mirror is extremely thin, and a cylindrical mirror needs to be added to the traditional LSU. The laser beam can be focused into a line (a point on the Y axis) through the cylindrical mirror and then projected on the reflector of the polygon mirror, so that the cost of components and the assembly process will be increased.

(3) The traditional polygon mirror must rotate at high speed (such as 40,000 rpm), resulting in relatively high rotation noise, and it takes a long time for the polygon mirror to start to work, increasing the waiting time after startup.

(4) In the assembly structure of the traditional LSU, the central axis of the laser beam projected to the reflector of the polygonal mirror is not directly facing the central rotation axis of the polygonal mirror, so that the off-axis of the polygonal mirror must be considered when designing the matching fθ lens The problem of off axis deviation relatively increases the trouble in the design and production of fθ lenses.

In recent years, in order to improve the problems of the traditional LSU assembly structure, an oscillating MEMS mirror has been developed on the market to replace the traditional polygonal mirror to control the laser beam scanning. Micro-electromechanical mirrors are torque oscillators (torsion oscillators), with a reflective layer attached to the surface, which can oscillate and swing the reflective layer to reflect light and scan. In the future, it will be used in imaging systems, scanners or laser printers. Scanning device (LSU for short), its scanning efficiency will be higher than the traditional rotating polygonal mirror. Such as U.S. Patents US6,844,951, US6,956,597 (generating at least one driving signal, the driving frequency of which is close to the resonant frequency of the complex MEMS mirrors, and driving the MEMS mirrors with a driving signal to generate a scanning path), US7, 064,876, US7,184,187, US7,190,499, US2006/0113393; or as Taiwan patent TW M253133 (between the collimating mirror and the fθ mirror in the LSU module structure, a micro-electromechanical mirror is used to replace the traditional rotating polygonal mirror, thereby controlling The projection direction of the laser beam); or such as Japanese patent JP 2006-201350, etc. The micro-electromechanical mirror has the advantages of small components, fast rotation speed and low manufacturing cost. However, due to the MEMS mirror, after receiving the voltage drive, it will perform simple harmonic motion (harmonic motion), and the way of this simple harmonic motion is a sinusoidal relationship between time and angular velocity, and projected on the MEMS mirror, after reflection The relationship between the reflection angle θ and time t is:

θ(t) = θ _s sin(2π f t) (1)

Among them: f is the scanning frequency of the MEMS mirror; θ _s is the maximum single-sided scanning angle of the laser beam after passing through the MEMS mirror.

Therefore, at the same time interval Δt, the corresponding reflection angle system changes as a sinusoidal function with time, that is, at the same time interval Δt, the reflection angle changes as: Δθ(t)=θ _s ·(sin(2π·f ·t ₁ )-sin(2π·f·t ₂ )), and has a nonlinear relationship with time, that is, when the reflected light is projected on the target at different angles, the light spots generated in the same time interval The distance intervals are not uniform and may increase or decrease over time.

For example, when the swing angle of the microelectromechanical mirror is at the peak and trough of the sine wave, the angle change will increase or decrease with time, which is different from the traditional polygonal mirror that rotates at a constant angular velocity. If the traditional fθ lens is used in the On the laser scanning unit (LSU) with micro-electro-mechanical mirrors, it will not be possible to correct the angle change produced by the micro-electro-mechanical mirrors, resulting in the phenomenon of non-constant-speed scanning of the laser beam projected on the imaging surface, resulting in imaging deviation. Therefore, the laser scanning device composed of micro-electro-mechanical mirrors is referred to as micro-electro-mechanical laser scanning device (MEMS LSU). Therefore, there is an urgent need to develop fθ mirrors that can be used in MEMS laser scanning devices to modify the scanning light so that images can be correctly imaged on the target object.

Contents of the invention

The purpose of the present invention is to provide a two-piece fθ lens of a MEMS laser scanning device. The two-piece fθ lens is counted sequentially from the MEMS reflector, and has a positive diopter crescent shape with a concave surface on the MEMS reflector side. It is composed of a negative diopter crescent-shaped lens with a convex surface on the side of the micro-electromechanical mirror, so that the scanning light reflected by the micro-electromechanical mirror can be correctly imaged on the target object, and the linear scanning required by the laser scanning device can be realized. Effect.

Another object of the present invention is to provide a two-piece fθ mirror of a micro-electromechanical laser scanning device, thereby reducing the area of the light spot projected on the target object and achieving the effect of improving resolution.

Another object of the present invention is to provide a two-piece fθ lens of a MEMS scanning device, which can correct the distortion due to the deviation of the scanning light from the optical axis, resulting in an increase in the deviation in the main scanning direction and the sub-scanning direction, so that The light spot formed on the photosensitive drum is deformed into an elliptical shape, and the size of each imaging light spot can be uniformed, so as to achieve the effect of improving the resolution quality.

Therefore, the two-piece fθ mirror of the micro-electro-mechanical laser scanning device of the present invention is suitable for at least one micro-electro-mechanical reflector that will oscillate the light source that emits the laser beam to resonate left and right to reflect the laser beam emitted by the light source into scanning light, so as to scan the target light. Imaging on the object; for laser printers, the target is often a photosensitive drum (drum), that is, when the imaging spot emits a laser beam through the light source, it is scanned left and right by the MEMS mirror, and the MEMS mirror reflects the laser beam to form Scanning light, the scanning light passes through the two-piece fθ lens of the present invention to correct the angle and position, and then forms a light spot on the photosensitive drum. Since the photosensitive drum is coated with a photosensitizer, it can sense the carbon powder and make it gather on the paper, so that the The data is printed out.

The two-piece fθ mirror of the present invention includes a first mirror and a second mirror that are counted sequentially from the micro-electromechanical mirror, wherein the first mirror has a first optical surface and a second optical surface, and the first optical surface is connected to the second optical surface. At least one optical surface in the main scanning direction of the two optical surfaces is composed of an aspheric surface, which is mainly used to change the distance between the light spots of the micro-electromechanical mirror with simple harmonic motion on the imaging surface from the original aspheric surface that decreases or increases with time. The constant-rate scanning phenomenon is corrected to equal-rate scanning, so that the projection of the laser beam on the imaging surface is equal-rate scanning. The second lens has a third optical surface and a fourth optical surface, and at least one optical surface of the third optical surface and the fourth optical surface in the main scanning direction is composed of an aspherical surface, which is mainly used to uniformize the scanning light in the The deviation of the optical axis in the main scanning direction and the sub scanning direction causes the imaging deviation formed on the photosensitive drum, and the scanning light of the first lens is corrected and focused on the target object.

Description of drawings

Fig. 1 is the schematic diagram of the optical path of the two-piece fθ lens of the present invention;

Fig. 2 is the relationship diagram of microelectromechanical mirror scanning angle θ and time t;

Fig. 3 is the optical path diagram and symbol description of the scanning light passing through the first lens and the second lens;

Fig. 4 is a schematic diagram showing that the area of the light spot changes with different projection positions after the scanning light is projected on the photosensitive drum;

Fig. 5 is a relation diagram of the Gaussian distribution of the light beam and the light intensity;

6 is an optical path diagram of an embodiment of the scanning light passing through the first lens and the second lens in the present invention;

Fig. 7 is a schematic diagram of light spots of the first embodiment;

Fig. 8 is a schematic diagram of light spots of the second embodiment;

Fig. 9 is a schematic diagram of light spots of the third embodiment;

Fig. 10 is a schematic diagram of light spots of the fourth embodiment; and

Fig. 11 is a schematic diagram of light spots of the fifth embodiment.

[Description of main component symbols]

10: MEMS mirror;

11: Laser light source;

111: light beam;

113a, 113b, 113c, 114a, 114b, 115a, 115b: scanning light;

131: first lens;

132: second lens;

14a, 14b: photoelectric sensors;

15: photosensitive drum;

16: Cylindrical mirror;

2, 2a, 2b, 2c: light spots; and

3: Effective scanning window.

Detailed ways

Please refer to FIG. 1. FIG. 1 is a schematic diagram of the optical path of the two-piece fθ lens of the MEMS laser scanning device of the present invention. The two-piece fθ mirror of the MEMS laser scanning device of the present invention includes a first mirror 131 with a first optical surface 131a and a second optical surface 131b, and a third optical surface 132a and a fourth optical surface. The second lens 132 of 132b is suitable for a MEMS laser scanning device. In the figure, the MEMS laser scanning device mainly includes a laser light source 11, a MEMS mirror 10, a cylindrical mirror 16, two photoelectric sensors 14a, 14b, and a photosensitive target. In the figure, the object is implemented with a photosensitive drum 15 . The light beam 111 generated by the laser light source 11 passes through the cylindrical mirror 16 and is projected onto the MEMS mirror 10 . The MEMS mirror 10 reflects the light beam 111 into scanning light rays 113 a , 113 b , 113 c , 114 a , 114 b , 115 a , and 115 b in a left-right resonant manner. Wherein the projection of the scanning rays 113a, 113b, 113c, 114a, 114b, 115a, 115b in the X direction is called the sub scanning direction (sub scanning direction), and the projection in the Y direction is called the main scanning direction (mainscanning direction), and The scanning angle of the MEMS mirror 10 is θc.

Please refer to FIG. 1 and FIG. 2 , wherein FIG. 2 is a relationship diagram between scanning angle θ and time t of the MEMS mirror. Since the micro-electromechanical mirror 10 is in simple harmonic motion, its motion angle changes sinusoidally with time, so the outgoing angle of the scanning light has a nonlinear relationship with time. As shown in the illustration, the wave peaks a-a' and wave troughs bb', their swing angles are obviously smaller than the wave bands a-b and a'-b', and this phenomenon of uneven angular velocity is likely to cause imaging deviation of the scanning light on the photosensitive drum 15 . Therefore, the photoelectric sensors 14a, 14b are arranged within ±θc of the maximum scanning angle of the microelectromechanical mirror 10, and its included angle is ±θp, and the laser beam begins to be reflected by the microelectromechanical mirror 10 from the peak of FIG. It is equivalent to the scanning light 115a of FIG. 1; when the photoelectric sensor 14a detects the scanning beam, it means that the micro-electromechanical mirror 10 swings to +θp angle, which is equivalent to the scanning light 114a of FIG. 1; when the micro-electromechanical mirror 10 When the scanning angle changes as point a in Figure 2, it is equivalent to the position of the scanning light 113b at this time; at this time, the laser light source 11 will be driven to emit a laser beam 111, and when scanning to point b in Figure 2, it is equivalent to the position of the scanning light ray The position of 113c (the laser beam 111 is emitted by the laser light source 11 within the corresponding ±θn angle); when the micro-electromechanical mirror 10 produces reverse vibration, such as being driven by the laser light source 11 in the wave band a'-b', it starts to emit laser light Beam 111; thus completing one cycle.

Please refer to FIG. 1 and FIG. 3 , wherein FIG. 3 is an optical path diagram of the scanning light passing through the first lens and the second lens. Among them, ±θn is the effective scanning angle. When the rotation angle of the MEMS mirror 10 enters ±θn, the laser light source 11 starts to emit the laser beam 111, which is reflected by the MEMS mirror 10 as scanning light. When the scanning light passes through the first mirror At 131 o'clock, it is refracted by the first optical surface 131a and the second optical surface 131b of the first mirror 131, and the scanning light reflected by the micro-electromechanical mirror 10, which has a nonlinear relationship between the distance and time, is converted into a scan with a linear relationship between distance and time. light. 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, thereby forming a row of light spots 2 on the photosensitive drum 15. On the photosensitive drum 15 , the distance between two farthest light spots 2 is called an effective scanning window 3 . Wherein, d1 is the distance from the MEMS mirror 10 to the first optical surface 131a, 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 (Curvature) of the first optical surface 131a, R2 is the second optical surface The radius of curvature of 131b, R3 is the radius of curvature of the third optical surface 132a, and R4 is the radius of curvature of the fourth optical surface 132b.

Please refer to Fig. 4, after the scanning light is projected on the photosensitive drum, in the spot area (spot area), Sa0 and Sb0 are the light spots of the scanning light on the reflection surface of the microelectromechanical mirror 10 in the main scanning direction (Y direction) And the length of the sub-scanning direction (X direction), Ga and Gb are Gaussian beams (Gaussian Beams) of scanning light at the light intensity of 13.5% in the Y direction and the beam radius of the X direction, as shown in Figure 5, in Figure 5 only Displays a description of the beam radius in the Y direction.

In summary, the two-piece fθ lens of the present invention can correct the scanning light reflected by the MEMS mirror 10, correct the scanning light of the Gaussian beam for distortion, and convert the relationship between time-angular velocity into time-distance Relationship. The light beams of the scanning light in the main scanning direction (Y direction) and the sub scanning direction (x direction) are amplified by the fθ lens, and light spots are generated on the imaging surface to provide a resolution that meets the requirements.

In order to achieve the above effects, the two-piece fθ lens of the present invention is 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 132b of the second lens 132, and on the main surface. The scanning direction or sub-scanning direction can be designed with a spherical surface or an aspheric surface. If an aspheric surface is used for design, the aspheric surface is the following surface equation:

1: Anamorphic equation

$\mathrm{<span\; class="notranslate">\; Z</span>}<span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; Cx</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; Cy</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="Y"\; filenames="H2008102104372E00031.png"\; state="\{\{state\}\}">Y</figure-callout></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>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; Cx</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</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">\; <figure-callout\; id="2"\; label="Y"\; filenames="H2008102104372E00031.png"\; state="\{\{state\}\}">Y</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}{<span\; class="notranslate">\; [</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; Y</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ]</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>$

${\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}{<span\; class="notranslate">\; [</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; Y</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ]</span>}^{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}{<span\; class="notranslate">\; [</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; Y</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ]</span>}^{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; +</span>$

${\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}{<span\; class="notranslate">\; [</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; Y</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ]</span>}^{\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Among them, Z is the distance from any point on the lens to the tangent plane of the origin in the direction of the optical axis (SAG); C _x and _Cy are the curvatures in the X direction and Y direction respectively; K _x and _Ky are the X direction and Y direction respectively The conic coefficient of the direction; A _R , B _R , C _R and _DR are the four, six, eight and ten power conic deformation coefficients (deformation from the conic) of the rotationally symmetrical portion, respectively ; A _P , B _P , C _P and D _P are the conic deformation coefficients (deformation from the conic) of the 4th, 6th, 8th, and 10th powers of non-rotationallysymmetric components, respectively; when C _x =C _y , K _x =K _y and A _P =B _p =C _p =D _p =0, it is simplified to a single aspheric surface.

2: Toric 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">\; <figure-callout\; id="2"\; label="Y"\; filenames="H2008102104372E00031.png"\; state="\{\{state\}\}">Y</figure-callout></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">\; <figure-callout\; id="2"\; label="Y"\; filenames="H2008102104372E00031.png"\; state="\{\{state\}\}">Y</figure-callout></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">\; 3</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 conic deformation coefficients of the fourth, sixth, eighth and tenth powers; when C _x =C _y and _Ky =A _P =B _p =C _p =D When _p = 0, it is simplified to a single sphere.

In order to keep the scanning light on the imaging surface of the target object at an equal scanning speed, for example, in two identical time intervals, the distance between the two light spots is kept equal; the two-piece fθ lens of the present invention can The light rays between the scanning light 113a and the scanning light 113b pass through the first lens 131 and the second lens 132 to correct the outgoing angle of the scanning light, so that the two scanning light at the same time interval, after the correction of the outgoing angle, will appear on the photosensitive image of the image. The distances between the two light spots formed on the drum 15 are equal. Furthermore, when the laser beam 111 is reflected by the microelectromechanical mirror 10, its Gaussian beam radius _Ga and _Gb are relatively large, if the scanning light passes through the distance between the microelectromechanical mirror 10 and the photosensitive drum 15, the Gaussian beam radius G _a and G _b will be larger, which does not meet the requirements of practical resolution; the two-piece fθ mirror of the present invention can further form G _a and G for the light between the scanning light 113a and the scanning light 113b reflected by the microelectromechanical mirror 10 _b less Gaussian light beams are focused on the photosensitive drum 15 of imaging to produce a smaller light spot; moreover, the two-piece fθ glass of the present invention can more uniformize the size of the light spot imaged on the photosensitive drum 15 ( limited to the range that meets the resolution requirements), in order to obtain the best resolution effect.

The two-piece fθ lens of the present invention includes, counting from the microelectromechanical mirror 10 in sequence, the first lens 131, which is a positive diopter crescent-shaped lens with a concave surface on the side of the microelectromechanical mirror 10, and the second lens 131. The two mirrors 132 are formed by a negative diopter crescent-shaped mirror with a convex surface on the side of the MEMS mirror; wherein the first mirror 131 has a first optical surface 131a and a second optical surface 131b, which are used for the MEMS mirror 10 The scanning light spot with the nonlinear relationship between the reflected angle and time is converted into the scanning light spot with a linear relationship between the distance and time; wherein the second mirror 132 has a third optical surface 132a and a fourth optical surface 132b for converting the first The scanning light of a mirror 131 is corrected and focused on the target; through the two-piece fθ mirror, the scanning light reflected by the micro-electromechanical mirror 10 is imaged on the photosensitive drum 15; wherein, the first optical surface 131a, the second optical The surface 131b, the third optical surface 132a, and the fourth optical surface 132b have at least one optical surface composed of an aspheric surface in the main scanning direction, the first optical surface 131a, the second optical surface 131b, the third optical surface 132a, and the fourth optical surface 132b. The four optical surfaces 132b may have at least one optical surface composed of an aspheric surface in the sub-scanning direction, or all optical surfaces composed of spherical surfaces may be used in the sub-scanning direction. Furthermore, regarding the composition of the first lens 131 and the second lens 132, in terms of optical effects, the two-piece fθ lens of the present invention further satisfies the conditions of formulas (4) to (5) in the main scanning direction:

$\mathrm{<span\; class="notranslate">\; 0.1</span>}<span\; class="notranslate">\; <</span>\frac{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="d"\; filenames="H2008102104372E00031.png"\; state="\{\{state\}\}">d</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; Y</span>}}}<span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; 1.2</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

$<span\; class="notranslate">\; <</span>\frac{{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; Y</span>}}}<span\; class="notranslate">\; <</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 0.01</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

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

$\mathrm{<span\; class="notranslate">\; 0.3</span>}<span\; class="notranslate">\; <</span><span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; s\; Y</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; (</span>\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}}}<span\; class="notranslate">\; +</span>\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span><span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; 0.6</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

And satisfy formula (7) in the sub-scanning direction

$\mathrm{<span\; class="notranslate">\; 0.1</span>}<span\; class="notranslate">\; <</span><span\; class="notranslate">\; |</span><span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; x</span>}}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; x</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}\mathrm{<span\; class="notranslate">\; x</span>}}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; x</span>}}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; sX</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; 1.1</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

Wherein, 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, _d3 is the first mirror 131 target object when θ=0° The distance from the side optical surface to the side optical surface of the second mirror 132 MEMS mirror 10, _d4 is the thickness of the second mirror 132 when θ=0°, _d5 is the second mirror 132 object side optics of the second mirror 132 when θ=0° The distance from the surface to the target object, f _sx is the composite focal length (combination focal length) of the two-piece fθ lens in the sub-scanning direction, f _sY is the composite focal length of the two-piece fθ lens in the main scanning direction, R _{ix is} the i-th optical surface The radius of curvature in the sub-scanning direction; R _iy is the radius of curvature of the i-th optical surface in the main scanning direction; n _d1 and n _d2 are the refraction indexes of the first lens 131 and the second lens 132 .

Furthermore, the uniformity of the light spot formed by the two-piece fθ lens of the present invention can be represented by the ratio δ of the maximum value and the minimum value of the beam size of the scanning light on the photosensitive drum 15, which satisfies the formula (8):

$\mathrm{<span\; class="notranslate">\; 0.8</span>}<span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; \&delta;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; min</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; max</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

Furthermore, the resolution formed by the two-piece fθ mirror of the present invention can use η _max to be the ratio of the maximum value of the light spot on the photosensitive drum 15 and η for the spot of the scanning light on the reflection surface of the microelectromechanical mirror 10 _Min is represented by the ratio of the light point of scanning light on the photosensitive drum 15 through scanning the light spot of scanning light on the reflective surface of microelectromechanical mirror 10, and can satisfy formula (9) and (10),

${\mathrm{<span\; class="notranslate">\; \&eta;</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; max</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; )</span>}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="0"\; label="S\; b"\; filenames="H2008102104372E00071.png,H2008102104372E00081.png"\; state="\{\{state\}\}">S</figure-callout></span><figure-callout\; id="0"\; label="S\; b"\; filenames="H2008102104372E00071.png,H2008102104372E00081.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; </span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; 0.10</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 9</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; \&eta;</span>}}_{\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; min</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; )</span>}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="0"\; label="S\; b"\; filenames="H2008102104372E00071.png,H2008102104372E00081.png"\; state="\{\{state\}\}">S</figure-callout></span><figure-callout\; id="0"\; label="S\; b"\; filenames="H2008102104372E00071.png,H2008102104372E00081.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; </span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; 0.10</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 10</span>}<span\; class="notranslate">\; )</span>$

Among them, S _a and S _b are the lengths of any light spot formed by scanning light on the photosensitive drum 15 in the Y direction and the X direction, δ is the ratio of the smallest light spot to the largest light spot on the photosensitive drum 15, and η is the microelectromechanical reflection Ratio of the light spot of the scanning light on the reflective surface of the mirror 10 to the light spot on the photosensitive drum 15; S _a0 and S _b0 are the lengths of the light spot of the scanning light on the reflective surface of the MEMS mirror 10 in the main scanning direction and the sub-scanning direction.

In order to make the present invention more definite and detailed, the preferred embodiments are listed hereby together with the following diagrams, and the structure and technical characteristics of the present invention are described in detail as follows:

The embodiments disclosed below of the present invention are described for the main components of the two-piece fθ lens of the MEMS laser scanning device of the present invention. Therefore, the embodiments disclosed below of the present invention are applied to the MEMS laser scanning device. However, as far as the general MEMS laser scanning device is concerned, except for the two-piece fθ lens disclosed in the present invention, other structures belong to the generally known technology, so those skilled in the art should understand that the MEMS disclosed in the present invention The components of the two-piece fθ lens of the laser scanning device are not limited to the structures disclosed in the following embodiments, that is, the components of the two-piece fθ lens of the MEMS laser scanning device can be changed in many ways, Modifications, or even equivalent changes, such as: radius of curvature design or surface design, material selection, distance adjustment, etc. of the first lens 131 and the second lens 132 are not limited.

<First embodiment>

Please refer to FIG. 6 , which is an optical path diagram of an embodiment of the scanning light passing through the first lens and the second lens of the present invention. The two-piece fθ lens of this embodiment has a first lens 131 and a second lens 132, wherein the first lens 131 is a crescent-shaped lens with a positive diopter and the concave surface is on the side of the MEMS mirror 10, and the second lens 132 is a negative diopter. The first lens 131 is a crescent-shaped lens with a concave surface on the side of the MEMS reflector 10, wherein the first optical surface 131a of the first lens 131 is The spherical surface, the second optical surface 131b, the third optical surface 132a and the fourth optical surface 132b of the second lens 132 are all aspheric surfaces, and the formula (2) is used to design the aspheric surface formula. Its optical properties and aspheric parameters are shown in Table 1 and Table 2.

Table 1 (fθ optical characteristics of the first embodiment)

optical surface Radius of curvature (mm) d Thickness (mm) n _dRefractive index MEMS reflective surface R0 ∞ 11.65 1

lens 1 1.527 R1 R1x 143.33 13.04 R1y -62.25 R2 (Anamorphic) R2x ^* -15.35 22.00 R2y ^* -36.88 lens 2 1.527 R3 (Anamorphic) R3x ^* 19.89 12.18 R3y ^* 223.38 R4 (Anamorphic) R4x ^* 75.52 89.76 R4y ^* 101.98 Photosensitive drum (drum) R5 ∞ 0.00

^* Denotes aspherical

Table two (the optical surface aspheric surface parameter of the first embodiment)

The two-piece fθ lens formed in this way, f(1)Y=145.78, f(2)Y=-368.67, fsX=23.655, fsY=215.37 (mm) can convert the scanning light into a linear relationship between distance and time Scan light spots, and scan the light spots Sa0=13.642 (μm) and Sb0=3718.32 (μm) on the micro-electromechanical mirror 10 to become scanning light, focus on the photosensitive drum 15 to form a smaller light spot 6, and Satisfy the conditions of formula (4) ~ formula (10), as shown in Table 3, the Gaussian beam diameter (μm) of the light spot on the photosensitive drum 15 with the central axis Z axis in the Y direction and the distance (mm) from the central axis Y, as shown in the table Four; and the light point distribution diagram of the present embodiment is as shown in FIG. 7 . In the figure, the diameter of the unit circle is 0.05mm.

Table three (the first embodiment satisfies the condition table)

Table 4 (the maximum value of the Gaussian beam diameter of the light spot on the photosensitive drum of the first embodiment)

Y -107.460 -96.206 -84.420 -96.206 -60.206 -48.050 -35.947 -23.914 0.000 Max(2Ga, 2Gb) 4.70E-03 3.75E-03 3.33E-03 3.48E-03 3.96E-03 4.13E-03 4.02E-03 3.43E-03 2.77E-03

<Second Embodiment>

The two-piece fθ lens of this embodiment includes a first lens 131 and a second lens 132, wherein the first lens 131 is a crescent-shaped lens with a positive diopter and the concave surface is on the side of the MEMS mirror 10, and the second lens 132 is a negative diopter. A crescent-shaped lens with a convex surface on the side of the microelectromechanical mirror 10, the first lens 131 is a lens with a crescent shape and a concave surface on the side of the microelectromechanical mirror 10, wherein the first optical surface 131a of the first lens 131 and the second The optical surface 131b is a spherical surface, and the third optical surface 132a of the second lens 132 is an aspherical surface, and the formula (2) is used to design an aspheric surface formula; the fourth optical surface 132b of the second lens 132 is an aspheric surface, and the formula (3) is used Designed for aspheric formulations. Its optical characteristics and aspherical parameters are shown in Table 5 and Table 6.

Table 5 (fθ optical characteristics of the second embodiment)

optical surface Radius of curvature (mm) d Thickness (mm) n _dRefractive index MEMS reflective surface R0 ∞ 12.42 1 Lens 1 1.527 R1 R1x 107.63 12.59 R1y -51.38 R2 R2x -15.74 11.37 R2y -32.25 Lens 2 1.527 R3 (Anamorphic) R3x ^* 19.26 8.00 R3y ^* 75.91 R4(Y Toroid) R4x 70.85 99.56 R4y ^* 45.26 Photosensitive drum (drum) R5 ∞ 0.00

^* Denotes aspherical

Table 6 (Aspherical parameters of the optical surface of the second embodiment)

Through the two-piece fθ lens formed here, f(1)Y=133.89, f(2)Y=-233.70, fsX=20.084, fsY=274.205 (mm) can convert the scanning light into linear distance and time Scan light spots, and scan light spots S _a0 =13.824 (μm) and S _b0 =3512.066 (μm) on the micro-electromechanical mirror 10 to become scanning light, focus on the photosensitive drum 15, and form smaller light spots 8 , and satisfy the conditions of (4) ~ formula (10), as shown in Table 7; on the photosensitive drum 15, the Gaussian beam diameter (μm) of the light spot with the central axis Z axis in the Y direction from the central axis Y distance (mm), such as Table 8; and the light point distribution diagram of this embodiment is shown in Figure 8. In the figure, the diameter of the unit circle is 0.05mm.

Table seven (the second embodiment satisfies the condition table)

Table 8. The maximum value of the Gaussian beam diameter of the light spot on the photosensitive drum of the second embodiment

Y -107.460 -96.206 -84.420 -96.206 -60.206 -48.050 -35.947 -23.914 0.000 Max(2Ga, 2Gb) 1.35E-02 1.27E-02 1.21E-02 1.28E-02 1.35E-02 1.41E-02 1.42E-02 1.37E-02 1.22E-02

<Third embodiment>

The first lens 131 and the second lens 132 of the two-piece fθ lens of this embodiment, wherein the first lens 131 is a lens with a positive diopter crescent shape and the concave surface is on the side of the MEMS mirror 10, and the second lens 132 is a negative diopter. The first lens 131 is a crescent-shaped lens with a concave surface on the side of the MEMS reflector 10, wherein the first optical surface 131a of the first lens 131 is The spherical surface, the second optical surface 131b, the third optical surface 132a and the fourth optical surface 132b of the second lens 132 are all aspheric surfaces, and the formula (2) is used to design the aspheric surface formula. Its optical characteristics and aspheric parameters are shown in Table 9 and Table 10.

Table nine (fθ optical characteristics of the third embodiment)

optical surface Radius of curvature (mm) dThickness (mm) n _dRefractive index MEMS reflective surface R0 ∞ 19.84 1 lens 1 1.527 R1 R1x -388.85 11.22 R1y -112.39 R2 (Anamorphic) R2x ^* -15.41 15.00 R2y ^* -42.77 lens 2 1.527 R3 (Anamorphic) R3x ^* 25.94 12.00 R3y ^* 422.59

R4 (Anamorphic) R4x ^* 56.93 94.18 R4y ^* 125.67 Photosensitive drum (drum) R5 ∞ 0.00

^* Denotes aspherical

Table 10 (Aspherical parameters of the optical surface of the third embodiment)

Through the two-piece fθ lens, f _(1)Y = 124.07, f _(2)Y = -344.01, f _sX = 23.785, f _sY = 176.355 (mm) can convert the scanning light into distance and time The light spot of the scanning light with a linear relationship, and the light spot S _a0 =13.452 (μm) and S _b0 =3941.106 (μm) on the micro-electromechanical mirror 10 are scanned to become the scanning light, which is focused on the photosensitive drum 15 to form a smaller Light spot 10, and satisfy the condition of (4) ~ formula (10), as table eleven; Gaussian beam diameter ( μm), as shown in Table 12; the light point distribution diagram of this embodiment is shown in Figure 9. In the figure, the diameter of the unit circle is 0.05 mm.

Table eleven (the third embodiment satisfies the condition table)

Table 12 (the maximum value of the Gaussian beam diameter of the light spot on the photosensitive drum of the third embodiment)

Y -107.458 -96.173 -84.419 -96.173 -60.343 -48.232 -36.136 -24.067 0.000 Max(2Ga, 2Gb) 3.75E-03 2.27E-03 1.89E-03 1.96E-03 3.05E-03 3.73E-03 3.92E-03 3.40E-03 1.84E-03

<Fourth Embodiment>

The first lens 131 and the second lens 132 of the two-piece fθ lens in this embodiment, wherein the first lens 131 is a crescent-shaped lens with a positive diopter and the concave surface is on the side of the micro-electromechanical mirror, and the second lens 132 is a new negative diopter. The first lens 131 is a crescent-shaped lens with a concave surface on the side of the MEMS reflector 10, wherein the first optical surface 131a of the first lens 131 is a spherical surface , the second optical surface 131b of the first lens 131 and the third optical surface 132a of the second lens 132 are both aspherical surfaces, and the formula (2) is used to design the aspheric surface formula; the fourth optical surface 132b of the second lens 132 is an aspheric surface For a spherical surface, formula (3) is used to design an aspheric surface formula. Its optical characteristics and aspherical parameters are shown in Table 13 and Table 14.

Table 13 (fθ optical characteristics of the fourth embodiment)

optical surface Radius of curvature (mm) dThickness (mm) n _dRefractive index MEMS reflective surface R0 ∞ 12.49 1 lens 1 1.527

R1 R1x 79.81 11.98 R1y -48.62 R2 (Anamorphic) R2x -15.47 10.00 R2y ^* -31.46 lens 2 1.527 R3 (Anamorphic) R3x 19.60 8.00 R3y ^* 62.12 R4(Y Toroid) R4x 71.71 101.12 R4y ^* 40.00 Photosensitive drum (drum) R5 0.00

^* Denotes aspherical

Table 14 (Optical Aspherical Parameters of the Fourth Embodiment)

Through this two-piece fθ lens, f _(1)Y = 136.21, f ₍₂₎ Y = -243.44, f _sX = 19.258, f _sY = 270.784 (mm), the scanning light can be converted into distance and time as Linear scanning light spots, and scan the light spots S _a0 = 13.81 (μm) and S _b0 = 3522.04 (μm) on the micro-electromechanical mirror 10 to become scanning light, which is focused on the photosensitive drum 15 to form a smaller light Point 12, and satisfy the conditions of (4) ~ formula (10), as shown in Table 15; on the photosensitive drum 15, the Gaussian beam diameter (μm) of the light spot with the central axis Z axis in the Y direction from the central axis Y distance (mm) ), as shown in Table 16; and the spot distribution diagram of the present embodiment is as shown in Figure 10. In the figure, the diameter of the unit circle is 0.05mm.

Table fifteen (the fourth embodiment satisfies the condition table)

Table 16 (Maximum value of spot Gaussian beam diameter on the photosensitive drum of the fourth embodiment)

Y -107.460 -96.206 -84.420 -96.206 -60.206 -48.050 -35.947 -23.914 0.000 Max(2Ga, 2Gb) 1.38E-02 1.28E-02 1.21E-02 1.28E-02 1.35E-02 1.40E-02 1.43E-02 1.39E-02 1.26E-02

<Fifth Embodiment>

The first lens 131 and a second lens 132 of the two-piece type fθ lens of the present embodiment, wherein the first lens 131 is a positive diopter crescent-shaped lens with a concave surface on the MEMS mirror 10 side, and the second lens 132 is a negative lens. Diopter crescent-shaped lenses with a convex surface on the side of the MEMS reflector 10, the first lens 131 is a lens with a crescent shape and a concave surface on the side of the MEMS reflector 10, the second optical surface 131b of the first lens 131 and the second optical surface 131b of the first lens 131 The 3rd optical surface 132a of two eyeglasses 132 is aspheric surface, uses formula (2) to be aspheric surface formula design; , use formula (3) to design the aspheric formula. Its optical characteristics and aspherical parameters are shown in Table 17 and Table 18.

Table 17 (fθ optical characteristics of the fifth embodiment)

optical surface Radius of curvature (mm) dThickness (mm) n _dRefractive index MEMS reflective surface R0 ∞ 30.74 1 lens 1 1.527 R1(Y Toroid) R1x -41.73 10.00 R1y ^* -39.34 R2 (Anamorphic) R2x ^* -11.19 12.95 R2y ^* -39.34 lens 2 1.527 R3 (Anamorphic) R3x ^* 347.39 12.00

R3y ^* 140.92 R4(Y Toroid) R4x 99.54 76.38 R4y ^* 124.52 Photosensitive drum (drum) R5 ∞ 0.00

^* Denotes aspherical

Table 18 (Aspherical parameters of the optical surface of the fifth embodiment)

Through the two-piece fθ lens formed here, f _(1)Y = 851.41, f _(2)Y = -2714.78, f _sX = 26.469, f _sY = 1221.728 (mm) can convert the scanning light into distance and time The light spot of the scanning light with a linear relationship, and the light spot S _a0 =14.31 (μm) and S _b0 =2983.85 (μm) on the micro-electromechanical mirror 10 are scanned to become the scanning light, which is focused on the photosensitive drum 15 to form a smaller Light spot 12, and satisfy the condition of (4) ~ formula (10), as table nineteen; Gaussian beam diameter ( μm), as shown in Table 20; and the light point distribution diagram of this embodiment is shown in Figure 11. In the figure, the diameter of the unit circle is 0.05mm.

Table nineteen (the fifth embodiment satisfies the condition table)

Table 20 (the maximum value of the Gaussian beam diameter of the light spot on the photosensitive drum of the fifth embodiment)

Y -107.460 -96.206 -84.420 -96.206 -60.206 -48.050 -35.947 -23.914 0.000

Max(2Ga, 2Gb) 1.35E-02 1.27E-02 1.21E-02 1.28E-02 1.35E-02 1.41E-02 1.42E-02 1.37E-02 1.22E-02

By above-mentioned description to embodiment, the present invention can reach following effect at least:

(1) By arranging the two-piece fθ mirror of the present invention, the point spacing of the micro-electromechanical reflector in simple harmonic motion can be corrected to equal speed by the original non-equal rate scanning phenomenon that decreases or increases with time. Speed scanning, the projection of the laser beam on the imaging surface is scanned at a constant speed, so that the distance between two adjacent light spots formed on the target object is equal.

(2) By arranging the two-piece fθ lens of the present invention, the distortion can be corrected to scan the light in the main scanning direction and the sub-scanning direction, so that the light spot focused on the imaging object can be reduced.

(3) By arranging the two-piece fθ lens of the present invention, 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 made uniform.

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

Claims (5)

1. the two-chip type f theta lens of a MEMS laser scanning device, it is applicable to MEMS laser scanning device, and this MEMS laser scanning device comprises a light source in order to the emission light beam, at least and swings in order to resonance and the beam reflection of light emitted is become mems mirror, and the object in order to sensitization of scanning ray; Begin to start in regular turn from this mems mirror, this two-chip type f theta lens comprise the crescent and concave surface of a positive diopter first eyeglass of this mems mirror side and a negative diopter is crescent and convex surface at second eyeglass of this mems mirror side, wherein this first eyeglass has one first optical surface and one second optical surface, this first optical surface and this second optical surface have at least an optical surface to be constituted by aspheric surface at main scanning direction, are used for converting the angle of this mems mirror reflection and the scanning ray luminous point of the nonlinear relationship of time to distance and linear scanning ray luminous point of time; Wherein this second eyeglass has one the 3rd optical surface and one the 4th optical surface, the 3rd optical surface and the 4th optical surface have at least an optical surface to be constituted by aspheric surface at main scanning direction, are used for the scanning ray correction of this first eyeglass is concentrated on this object; By this two-chip type f theta lens, make scanning ray imaging on this object of this mems mirror reflection.

2. the two-chip type f theta lens of MEMS laser scanning device as claimed in claim 1, wherein, described two-chip type f theta lens further satisfies following condition at main scanning direction:

$0.1<\frac{d_3+d_4+d_5}{f_{\left(1\right)Y}}<1.2;$

$-0.6<\frac{d_5}{f_{\left(2\right)Y}}<-0.01;$

Wherein, f _{(1) Y}Be focal length, the f of this first eyeglass at main scanning direction _{(2) Y}Be focal length, the d of this second eyeglass at main scanning direction ₃This first eyeglass object side optical surface is to distance, the d of this second eyeglass mems mirror side optical surface during for θ=0 ° ₄Thickness, the d of this second eyeglass during for θ=0 ° ₅This second eyeglass object side optical surface is to the distance of this object during for θ=0 °.

3. the two-chip type f theta lens of MEMS laser scanning device as claimed in claim 1, wherein, described two-chip type f theta lens further satisfies following condition:

Satisfy at main scanning direction

$0.3<|f_{\mathrm{sY}}\&CenterDot;(\frac{n_{d1}-1}{f_{\left(1\right)y}}+\frac{(n_{d2}-1)}{f_{\left(2\right)y}})|<0.6;$

Satisfy at sub scanning direction

$0.1<|(\frac{1}{R_{1x}}-\frac{1}{R_{2x}})+(\frac{1}{R_{3x}}-\frac{1}{R_{4x}})f_{\mathrm{sX}}|<1.1;$

Wherein, f _{(1) Y}With f _{(2) Y}Be this first eyeglass and this second eyeglass focal length, f at main scanning direction _SXBe compound focal length, the f of two-chip type f theta lens at sub scanning direction _SYBe compound focal length, the R of two-chip type f theta lens at main scanning direction _IxBe radius-of-curvature, the n of i optical surface at sub scanning direction _D1With n _D2Be respectively the refractive index of this first eyeglass and this second eyeglass.

4. the two-chip type f theta lens of MEMS laser scanning device as claimed in claim 1, wherein, the ratio of maximum luminous point and smallest spot size satisfies on this object:

$0.8<\mathrm{\&delta;}=\frac{\min (S_b\&CenterDot;S_a)}{\max (S_b\&CenterDot;S_a)};$

Wherein, Sa and Sb are scanning ray forms on the object any luminous point at the length of main scanning direction and sub scanning direction, the δ ratio for smallest spot on this object and maximum luminous point.

5. the two-chip type f theta lens of MEMS laser scanning device as claimed in claim 1, wherein, the ratio of maximum luminous point satisfies respectively with the ratio of smallest spot on this object on this object:

${\mathrm{\&eta;}}_{\max }=\frac{\max (S_b\&CenterDot;S_a)}{(S_{b0}\&CenterDot;S_{a0})}<0.10;$

${\mathrm{\&eta;}}_{\min }=\frac{\min (S_b\&CenterDot;S_a)}{(S_{b0}\&CenterDot;S_{a0})}<0.10;$

Wherein, S _A0With S _B0Be the luminous point of scanning ray on this mems mirror reflecting surface length, S at main scanning direction and sub scanning direction _aWith S _bBe length, the η of any luminous point of scanning ray formation on the object at main scanning direction and sub scanning direction _MaxBe the luminous point of scanning ray on this mems mirror reflecting surface ratio, η through scanning maximum luminous point on this object _MinBe the luminous point of scanning ray on this mems mirror reflecting surface ratio through scanning smallest spot on this object.

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