CN101650473B - Two-element ftheta lens for MEMS laser scanning unit - Google Patents

Abstract

A two-element ftheta lens of an MEMS laser scanning unit comprises a biconvex first lens and a biconcave second lens, wherein, the first lens has two optical surfaces, at least one of which is formed by an aspheric surface in the main scanning direction and is mainly used for converting the spots of the scanning rays which are reflected by the MEMS mirror and have angles in non-linear relations with time into the spots of the scanning rays which have distances in linear relations with time; the second lens has two optical surfaces, at least one of which is formed by an aspheric surface in the main scanning direction and is mainly used for correcting and condensing the scanning rays of the first lens on the objects. Besides, both the first lens and the second lens satisfy the specific optical conditions and can achieve the purposes of linear scanning effect and high-resolution scanning.

Description

The two-chip type f theta lens of MEMS laser scanning device

Technical field

The present invention relates to a kind of two-chip type f theta lens of MEMS laser scanning device, be particularly related to and a kind ofly be the mems mirror of simple harmonic characteristic motion and produce the angle variable quantity that becomes sine relation in time, to realize the two-chip type f theta lens of the desired linear sweep effect of laser scanning device in order to correction.

Background technology

The present used laser scanning device LSU (Laser Scanning Unit) of laser beam printer LBP (Laser Beam Print), be the scanning motion (laser beam scanning) of polygonal mirror (polygon mirror) that utilizes a high speed rotating to control laser beam, as U.S. Pat 7079171, US6377293, US6295116, or as described in the patent I198966 of Taiwan.The following summary of its principle: utilize semiconductor laser give off laser beam (laser beam), earlier via a collimating mirror (collimator), form parallel beam again via an aperture (aperture), and parallel beam is again through behind the cylindrical mirror (cylindrical lens), width on the Y-axis of sub scanning direction (sub scanning direction) can be along the parallel focusing of parallel direction of the X-axis of main scanning direction (mainscanning direction) and is formed a wire imaging (line image), be projected to again on the polygonal mirror of a high speed rotating, and evenly being provided with polygonal mirror on the polygonal mirror continuously, it just is positioned at or approaches the focal position of above-mentioned wire imaging (line image).Projecting direction by polygonal mirror control laser beam, when continuous a plurality of catoptrons during at high speed rotating can be incident upon on the catoptron laser beam along the parallel direction of main scanning direction (X-axis) with same tarnsition velocity (angular velocity) deflective reflector to f θ linear sweep eyeglass on, and f θ linear sweep eyeglass is arranged at the polygonal mirror side, can be single-piece lens structure (single-element scanning lens) or is two formula lens structures.The function of this f θ linear sweep eyeglass is to make the laser beam of injecting the f Theta lens via the mirror reflects on the polygonal mirror can be focused into an ellipse luminous point and be incident upon a light receiving surface (photoreceptor drum, be imaging surface) on, and the requirement of realization linear sweep (scanning linearity).Yet the laser scanning device LSU of prior art has following point in the use:

(1) the manufacture difficulty height of rotary multi mirror and price are not low, increase the cost of manufacture of LSU relatively.

(2) polygonal mirror palpus tool high speed rotating (as 40000 rev/mins) function, precision requirement is high again, so that the minute surface Y-axis width of reflecting surface as thin as a wafer on the general polygonal mirror, make and all need set up a cylindrical mirror (cylindrical lens) among the LSU of prior art, so that increase member cost and assembling operation flow process so that laser beam can focus on being aligned (becoming a bit on the Y-axis) through cylindrical mirror and be incident upon on the catoptron of polygonal mirror again.

(3) polygonal mirror of prior art must high speed rotating (as 40000 rev/mins), cause Rotation Noise and improve relatively, and polygonal mirror must expend the long period from starting to working speed, increases the stand-by period of start back.

(4) in the package assembly of the LSU of prior art, the laser beam central shaft that is projected to the polygonal mirror catoptron is not the central rotating shaft over against polygonal mirror, so that when the f Theta lens that design matches, need consider simultaneously polygonal mirror from axle deviation (off axis deviation) problem, increase the design of f Theta lens relatively and make to go up trouble.

In recent years since,, developed the mems mirror (MEMS mirror) of a kind of swing type (oscillatory) at present on the market, control laser beam flying in order to the polygonal mirror that replaces prior art for the problem of the LSU package assembly of improving prior art.Mems mirror is torque oscillation device (torsion oscillators), has reflector layer on its top layer, can be by vibration swing reflector layer, the light reflection is scanned, to can be applicable to laser scanning device (the laser scanning unit of image system (imaging system), scanner (scanner) or laser printer (laserprinter) future, be called for short LSU), its scan efficiency (Scanningefficiency) can be higher than traditional polygonal rotating mirror.As U.S. Pat 6,844,951, US6,956,597 (producing at least one drive signal, the resonant frequency of a plurality of mems mirrors of its driving frequency convergence, and drive signal with and drive mems mirror), US7 to produce the one scan path, 064,876, US7,184,187, US7,190,499, US2006/0113393; Or, in a LSU modular structure, between collimating mirror and the f Theta lens, utilize the rotary multi mirror of mems mirror replacement prior art as Taiwan patent TW M253133, control the projecting direction of laser beam thus; Or as Jap.P. JP2006-201350 etc.This mems mirror has that assembly is little, and velocity of rotation is fast, advantage of low manufacturing cost.Yet because mems mirror, after receiving a driven, will do a simple harmonic motion (harmonicmotion), and the mode of this simple harmonic motion is that time and angular velocity are sine relation, and be projeced into mems mirror, its after reflection reflection angle θ and the pass of time t be:

θ(t)＝θ _s·sin(2π·f·t) (1)

Wherein: f is the sweep frequency of mems mirror; θ _sScanning angle for laser beam monolateral maximum behind mems mirror.

Therefore, Δ t under the identical time interval, pairing reflection angle system becomes sine function (Sinusoidal) variation with the time, and promptly when identical time interval Δ t, reflection angle is changed to: Δ θ (t)=θ _s(sin (2 π ft ₁)-sin (2 π ft ₂)), and be nonlinear relationship, that is the spot distance that is produced is at interval and inequality and increasing or decreasing in time in the identical time interval when the light of this reflection is incident upon object with different angles with the time.

For example, when the pendulum angle of mems mirror is positioned at the crest of sine wave and trough, angle variable quantity is increasing or decreasing in time, different with the mode of motion that the polygonal mirror of prior art becomes constant angular velocity to rotate, if have the upward f Theta lens of use prior art of the laser scanning device of mems mirror (LSU), can't revise the angle variable quantity that mems mirror produces, and cause the laser light velocity that is incident upon on the imaging surface will produce speed scanning phenomenon such as non-and produce the imaging deviation that is positioned on the imaging surface.Therefore, for the laser scanning device that mems mirror constituted, abbreviate MEMS laser scanning device (MEMS LSU) as, its characteristic is after laser beam scans via mems mirror, form the not equal angular scanning ray of constant duration, therefore development can be used in MEMS laser scanning device the f Theta lens to revise scanning ray, making can correct imaging on object, will be for urgently required.

Summary of the invention

The object of the present invention is to provide a kind of two-chip type f theta lens of MEMS laser scanning device, this two-chip type f theta lens is started in regular turn by mems mirror, sending out second eyeglass by one lenticular first eyeglass and a double concave is constituted, can be with the correct imaging on object of scanning ray that mems mirror reflected, thus realize the desired linear sweep effect of laser scanning device.

Another object of the present invention is to provide a kind of two-chip type f theta lens of MEMS laser scanning device, in order to dwindling the area that is incident upon luminous point on the object (spot), thereby realize improving the effect of resolution.

A further object of the present invention is to provide a kind of two-chip type f theta lens of MEMS laser scanning device, the modifying factor that can distort scanning ray departs from optical axis, and cause skew to increase at main scanning direction and sub scanning direction, make the luminous point that images in photosensitive drums be deformed into the oval-shaped problem of class, and make each imaging luminous point size be able to homogenising, thereby realize promoting the effect of resolution quality (resolution quality).

Therefore, the two-chip type f theta lens of MEMS laser scanning device of the present invention, be applicable to that comprising one at least swings the light source of emission of lasering beam and the laser beam reflection of light emitted to be become the mems mirror of scanning ray with resonance, with imaging on object; For laser printer, this object often is a photosensitive drums (drum), that is, treat that the luminous point of imaging gives off laser beam via light source, via scanning about mems mirror, the mems mirror reflection lasering beam forms scanning ray, scanning ray via two-chip type f theta lens angle correction of the present invention and position after, on photosensitive drums, form luminous point (spot), because photosensitive drums scribbles photosensitizer, can respond to carbon dust it is gathered on the paper, so data can be printed.

Two-chip type f theta lens of the present invention comprises by mems mirror one of starts at first eyeglass and one second eyeglass in regular turn, wherein first eyeglass has one first optical surface and one second optical surface, first optical surface and second optical surface have at least an optical surface to be constituted by aspheric surface at main scanning direction, the mems mirror that mainly will be simple harmonic motion, the speed scanning phenomenon such as non-of successively decreasing by originally increasing in time or increasing progressively at imaging surface glazing dot spacing, speed scanning such as be modified to, make speed such as the projection work scanning of laser beam at imaging surface.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, it is poor mainly in photosensitive drums on to be formed into kine bias at main scanning direction and sub scanning direction because of the skew optical axis causes in order to the homogenising scanning ray, and the scanning ray correction of first eyeglass is concentrated on the object.

Description of drawings

Fig. 1 is the synoptic diagram of the optical path of two-chip type f theta lens of the present invention;

Fig. 2 is the graph of a relation of a mems mirror scanning angle θ and time t;

Fig. 3 is by the optical path figure of the scanning ray of first eyeglass and second eyeglass and symbol description figure;

Fig. 4 is after scanning ray is incident upon on the photosensitive drums, the synoptic diagram that spot areas changes with the difference of launching position;

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

Fig. 6 is the optical path figure of the embodiment of the scanning ray that passes through first eyeglass and second eyeglass of the present invention;

Fig. 7 is the luminous point synoptic diagram of first embodiment;

Fig. 8 is the luminous point synoptic diagram of second embodiment;

Fig. 9 is the luminous point synoptic diagram of the 3rd embodiment; And

Figure 10 is the luminous point synoptic diagram of the 4th embodiment.

The primary clustering symbol description:

10: mems mirror;

11: LASER Light Source;

111: light beam;

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

131: the first eyeglasses;

132: the second eyeglasses;

14a, 14b: photoelectric sensor;

15: photosensitive drums;

16: cylindrical mirror;

2,2a, 2b, 2c: luminous point; And

3: the effective scanning window

Embodiment

With reference to Fig. 1, Fig. 1 is the synoptic diagram of optical path of the two-chip type f theta lens of MEMS laser scanning device of the present invention.The two-chip type f theta lens of MEMS laser scanning device of the present invention comprises first eyeglass 131 with the first optical surface 131a and second optical surface 131b, and second eyeglass 132 with the 3rd optical surface 132a and the 4th optical surface 132b, be applicable to MEMS laser scanning device.Among the figure, MEMS laser scanning device mainly comprises a LASER Light Source 11, a mems mirror 10, a cylindrical mirror 16, two photoelectric sensor 14a, 14b, and an object in order to sensitization.In the drawings, object uses photosensitive drums (drum) 15 to implement.The light beam 111 that LASER Light Source 11 is produced projects on the mems mirror 10 by behind the cylindrical mirror 16.And the mode that mems mirror 10 swings with resonance is reflected into scanning ray 113a, 113b, 113c, 114a, 114b, 115a, 115b with light beam 111. Wherein scanning ray 113a, 113b, 113c, 114a, 114b, 115a, 115b are referred to as sub scanning direction (sub scanning direction) in the projection of directions X, projection in the Y direction is referred to as main scanning direction (main scanning direction), and mems mirror 10 scanning angles are θ c.

With reference to Fig. 1 and Fig. 2, wherein Fig. 2 is the graph of a relation of mems mirror scanning angle θ and time t.Because mems mirror 10 is simple harmonic motion, its movement angle is sinusoidal variations in time, so the ejaculation angle of scanning ray and time are nonlinear relationship.Crest a-a ' as shown and trough b-b ', its pendulum angle are significantly less than wave band a-b and a '-b ', and the unequal phenomenon of this angular velocity causes scanning ray to produce the imaging deviation easily on photosensitive drums 15.Therefore, photoelectric sensor 14a, 14b are arranged within mems mirror 10 maximum scans angle ± θ c, and its angle is ± θ p that laser beam is begun to be reflected by mems mirror 10 by the crest place of Fig. 2, is equivalent to the scanning ray 115a of Fig. 1 this moment; When photoelectric sensor 14a detected scanning light beam, expression mems mirror 10 swung to+θ p angle, was equivalent to the scanning ray 114a of Fig. 1 this moment; When mems mirror 10 scanning angles change as during a point of Fig. 2, are equivalent to scanning ray 113b position at this moment; LASER Light Source 11 will be driven and give off laser beam 111 this moment, and when being scanned up to the b point of Fig. 2, be equivalent to scanning ray 113c position at this moment till (being equivalent in ± θ n angle, give off laser beam 111) by LASER Light Source 11; When mems mirror 10 produces reversals of vibrations, as being driven by LASER Light Source 11 when the wave band a '-b ' and beginning to give off laser beam 111; So finish one-period.

With reference to Fig. 1 and Fig. 3, wherein Fig. 3 is the optical path figure by the scanning ray of first eyeglass and second eyeglass.Wherein, ± θ n is the effective scanning angle, when the rotational angle of mems mirror 10 enter ± during θ n, LASER Light Source 11 begins to give off laser beam 111, be reflected into scanning ray via mems mirror 10, when scanning ray is reflected by the first optical surface 131a of first eyeglass 131 and the second optical surface 131b during by first eyeglass 131, it is the scanning ray of linear relationship with the time with the time that the distance that mems mirror 10 is reflected becomes the scanning ray of nonlinear relationship to convert distance to.After scanning ray is by first eyeglass 131 and second eyeglass 132, optical property by the first optical surface 131a, the second optical surface 131b, the 3rd optical surface 132a, the 4th optical surface 132b, scanning ray is focused on the photosensitive drums 15, and on photosensitive drums 15, form a luminous point (Spot) 2 that is listed as.On photosensitive drums 15, two farthest the spacing of luminous point 2 be called effective scanning window 3.Wherein, d ₁Spacing, d for mems mirror 10 to first optical surface 131a ₂Be spacing, the d of first optical surface 131a to the second optical surface 131b ₃Be spacing, the d of the second optical surface 131b to the, three optical surface 132a ₄Be spacing, the d of the 3rd optical surface 132a to the four optical surface 132b ₅Be spacing, the R of the 4th optical surface 132b to photosensitive drums 15 ₁Be radius-of-curvature (Curvature), the R of the first optical surface 131a ₂Be radius-of-curvature, the R of the second optical surface 131b ₃Be radius-of-curvature and the R of the 3rd optical surface 132a ₄It is the radius-of-curvature of the 4th optical surface 132b.

With reference to Fig. 4, Fig. 4 is after scanning ray is incident upon on the photosensitive drums, the synoptic diagram that spot areas (spot area) changes with the difference of launching position.When scanning ray 113a is incident upon photosensitive drums 15 after optical axis direction sees through first eyeglass 131 and second eyeglass 132, because be incident in the angle of first eyeglass 131 and second eyeglass 132 is zero, so in the deviation ratio that main scanning direction produced is zero, therefore the luminous point 2a that images on the photosensitive drums 15 is a similar round.When scanning ray 113b and 113c see through first eyeglass 131 and second eyeglass, 132 backs and when being incident upon photosensitive drums 15, because it is non-vanishing to be incident in first eyeglass 131 and second eyeglass 132 and the formed angle of optical axis, so non-vanishing in the deviation ratio that main scanning direction produced, and cause in the projected length of main scanning direction bigger than the formed luminous point of scanning ray 113a; This situation is also identical at sub scanning direction, and the formed luminous point of scanning ray that departs from scanning ray 113a also will be bigger; So the luminous point 2b, the 2c that image on the photosensitive drums 15 are a class ellipse, and the area of 2b, 2c is greater than 2a.Wherein, S _A0With S _B0Be length, the G of the luminous point of scanning ray on mems mirror 10 reflectings surface at main scanning direction (Y direction) and sub scanning direction (directions X) _aWith G _bThe Gaussian beam (Gaussian Beams) that is scanning ray is 13.5% to be in the beam radius of Y direction and directions X in light intensity, as shown in Figure 5, only shows the explanation of the beam radius of Y direction among Fig. 5.

In sum, two-chip type f theta lens of the present invention can be with the scanning ray of mems mirror 10 reflection, that is, with the scanning ray of Gaussian beam distort (distortion) revise, and the relation of time-angular velocity is changed into the relation of time-distance.Scanning ray is exaggerated at the light beam of main scanning direction (Y direction) with sub scanning direction (directions X), produces luminous point on imaging surface, so that the resolution that meets demand to be provided.

For realizing above-mentioned effect, two-chip type f theta lens of the present invention is at the first optical surface 131a of first eyeglass 131 or the 3rd optical surface 132a or the 4th optical surface 132b of the second optical surface 132a and second eyeglass 132, at main scanning direction or sub scanning direction, can use the design of sphere curved surface or non-spherical surface, if use the non-spherical surface design, then non-spherical surface is following surface equation formula:

1: horizontal picture surface equation formula (Anamorphic equation)

$Z=\frac{\left(\mathrm{Cx}\right)X^2+\left(\mathrm{Cy}\right){\mathrm{<figure-callout\; id="2"\; label="Y"\; filenames="H2008102104391E00031.png"\; state="\{\{state\}\}">Y</figure-callout>}}^2}{1+\sqrt{1-(1+\mathrm{Kx}){\left(\mathrm{Cx}\right)}^2{X}^2-(1+\mathrm{Ky}){\left(\mathrm{Cy}\right)}^2{\mathrm{<figure-callout\; id="2"\; label="Y"\; filenames="H2008102104391E00031.png"\; state="\{\{state\}\}">Y</figure-callout>}}^2}}+A_R{[(1-A_P)X^2+(1+A_P)Y^2]}^2+$

$B_R{[(1-B_P)X^2+(1+B_P)Y^2]}^3+C_R{[(1-C_P)X^2+(1+C_P)Y^2]}^4+$

$D_R{[(1-D_P)X^2+(1+D_P)Y^2]}^5---\left(2\right)$

Wherein, Z be on the eyeglass any point with the distance (SAG) of optical axis direction to the initial point section; C _xWith C _yBe respectively the curvature (curvature) of directions X and Y direction; K _xWith K _yBe respectively the circular cone coefficient (Conic coefifcient) of directions X and Y direction; A _R, B _R, C _RWith D _RBe respectively the circular cone deformation coefficient (deformationfrom the conic) with ten powers four times, six times, for eight times of rotation symmetry (rotationallysymmetric portion); A _P, B _P, C _PWith D _PBe respectively the circular cone deformation coefficient (deformation from the conic) of four times, six times, eight times, ten times powers of non-rotating symmetry (non-rotationallysymmetric components); Work as C _x=C _y, K _x=K _yAnd A _P=B _p=C _p=D _p, be reduced to single aspheric surface at=0 o'clock.

2: ring is as surface equation formula (Toric equation)

$Z=\mathrm{Zy}+\frac{\left(\mathrm{Cxy}\right){\mathrm{<figure-callout\; id="2"\; label="X"\; filenames="H2008102104391E00031.png"\; state="\{\{state\}\}">X</figure-callout>}}^2}{1+\sqrt{1-{\left(\mathrm{Cxy}\right)}^2{\mathrm{<figure-callout\; id="2"\; label="X"\; filenames="H2008102104391E00031.png"\; state="\{\{state\}\}">X</figure-callout>}}^2}}$

$\mathrm{Cxy}=\frac{1}{(1/\mathrm{Cx})-\mathrm{Zy}}$

$\mathrm{Zy}=\frac{\left(\mathrm{Cy}\right){\mathrm{<figure-callout\; id="2"\; label="Y"\; filenames="H2008102104391E00031.png"\; state="\{\{state\}\}">Y</figure-callout>}}^2}{1+\sqrt{1-(1+\mathrm{Ky}){\left(\mathrm{Cy}\right)}^2{\mathrm{<figure-callout\; id="2"\; label="Y"\; filenames="H2008102104391E00031.png"\; state="\{\{state\}\}">Y</figure-callout>}}^2}}+B_4{Y}^4+B_6{Y}^6+B_8{Y}^8+B_{10}{Y}^{10}---\left(3\right)$

Wherein, Z be on the eyeglass any point with the distance (SAG) of optical axis direction to the initial point section; C _yWith C _xThe curvature (curvature) of difference Y direction and directions X; K _yCircular cone coefficient (Coniccoefficient) for the Y direction; B ₄, B ₆, B ₈With B ₁₀It is the circular cone deformation coefficient (4th～10th order coefficients) (dedormation from the conic) of four times, six times, eight times, ten times powers; Work as C _x=C _yAnd K _y=A _P=B _p=C _p=D _p, be reduced to single sphere at=0 o'clock.

In order to make scanning ray sweep velocity such as keep on the imaging surface on the object, for example, in two identical time intervals, the spacing of keeping two luminous points equates; Two-chip type f theta lens of the present invention can carry out the correction of scanning ray emergence angle by first eyeglass 131 and second eyeglass 132 to the light between the scanning ray 113b with scanning ray 113a, make two scanning rays in the identical time interval, after the shooting angle correction, the distance of two luminous points that form on the photosensitive drums 15 of imaging equates.Further, after laser beam 111 was via mems mirror 10 reflections, its Gaussian beam radius Ga and Gb were bigger, if after the distance of this scanning ray through mems mirror 10 and photosensitive drums 15, Gaussian beam radius Ga and Gb will be bigger, not meet practical resolution requirement; Two-chip type f theta lens of the present invention further can form Ga and the less Gaussian beam of Gb to the light between the scanning ray 113b with the scanning ray 113a of mems mirror 10 reflection, focus on then and on the photosensitive drums 15 of imaging the less luminous point of generation; Moreover two-chip type f theta lens of the present invention more can be with the luminous point size homogenising (being limited to meets in the scope of resolution requirement) that is imaged on the photosensitive drums 15, to get best resolution effect.

Two-chip type f theta lens of the present invention comprises, start in regular turn by mems mirror 10, be first eyeglass 131 and second eyeglass 132, being lenticular eyeglass constitutes, wherein first eyeglass 131 has the first optical surface 131a and the second optical surface 131b, with the angle of mems mirror 10 reflection become with the time scanning ray luminous point of nonlinear relationship convert to apart from the time be the scanning ray luminous point of linear relationship; Wherein, second eyeglass 132 has the 3rd optical surface 132a and the 4th optical surface 132b, and the scanning ray correction of first eyeglass 131 is concentrated on the object; By of scanning ray in photosensitive drums 15 on the imaging of this two-chip type f theta lens with mems mirror 10 reflections; Wherein, the first optical surface 131a, the second optical surface 131b, the 3rd optical surface 132a and the 4th optical surface 132b have at least one to be optical surface that aspheric surface constituted at main scanning direction, and the first optical surface 131a, the second optical surface 131b, the 3rd optical surface 132a and the 4th optical surface 132b can have at least one to be optical surface that aspheric surface constituted or the optical surface that all uses sphere and constituted at sub scanning direction at sub scanning direction.Further, on first eyeglass 131 and second eyeglass, 132 formations, on optical effect, two-chip type f theta lens of the present invention, further satisfy formula (4)～formula (5) condition at main scanning direction:

$1.6<\frac{{\mathrm{<figure-callout\; id="3"\; label="d"\; filenames="H2008102104391E00031.png"\; state="\{\{state\}\}">d</figure-callout>}}_3+d_4+d_5}{f_{\left(1\right)Y}}<2.5---\left(4\right)$

$-2.0<\frac{d_5}{f_{\left(2\right)Y}}<-1.0---\left(5\right)$

Or satisfy formula (6) at main scanning direction

$0.2<|f_{\mathrm{sY}}\&CenterDot;(\frac{(n_{d1}-1)}{f_{\left(1\right)y}}+\frac{(n_{d2}-1)}{d_{\left(2\right)y}})|<0.4---\left(6\right)$

And satisfy formula (7) at sub scanning direction

$0.8<|(\frac{1}{R_{1x}}-\frac{1}{R_{2x}})+(\frac{1}{R_{3x}}-\frac{1}{R_{4x}})f_{\mathrm{sX}}|<1.6---\left(7\right)$

Wherein, f _{(1) Y}Be the focal length of first eyeglass 131 at main scanning direction, f _{(2) Y}Be the focal length of second eyeglass 132 at main scanning direction, d ₃The distance of first eyeglass, 131 object side optical surface to the second eyeglasses, 132 mems mirrors, 10 side optical surfaces during for θ=0 °, d ₄Second eyeglass, 132 thickness during for θ=0 °, d ₅Second eyeglass, 132 object side optical surfaces are to the distance of object, f during for θ=0 ° _SxBe the compound focal length (combination focal length) of two-chip type f theta lens at sub scanning direction, f _SYBe the compound focal length of two-chip type f theta lens at main scanning direction, R _IxBe the radius-of-curvature of i optical surface at sub scanning direction; R _IyBe the radius-of-curvature of i optical surface at main scanning direction; n _D1With n _D2It is the refractive index (refraction index) of first eyeglass 131 and second eyeglass 132.

Moreover the formed luminous point homogeneity of two-chip type f theta lens of the present invention can be represented by the maximal value of the beam size of scanning ray on photosensitive drums 15 and the ratio delta of minimum value, promptly satisfies formula (8):

$0.8<\mathrm{\&delta;}=\frac{\min (S_b\&CenterDot;S_a)}{\max (S_b\&CenterDot;S_a)}---\left(8\right)$

Further, the formed resolution of two-chip type f theta lens of the present invention can be used η _MaxFor the luminous point of scanning ray on mems mirror 10 reflectings surface through the scanning peaked ratio of luminous point and η on photosensitive drums 15 _MinRepresent through scanning ratio of luminous point minimum value on photosensitive drums 15 for the luminous point of scanning ray on mems mirror 10 reflectings surface, can satisfy formula (9) and (10),

${\mathrm{\&eta;}}_{\max }=\frac{\max (S_b\&CenterDot;S_a)}{({\mathrm{<figure-callout\; id="0"\; label="S\; b"\; filenames="H2008102104391E00011.png,H2008102104391E00071.png"\; state="\{\{state\}\}">S</figure-callout>}}_b\&CenterDot;S_{a0})}<0.10---\left(9\right)$

${\mathrm{\&eta;}}_{\min }=\frac{\min (S_b\&CenterDot;S_a)}{({\mathrm{<figure-callout\; id="0"\; label="S\; b"\; filenames="H2008102104391E00011.png,H2008102104391E00071.png"\; state="\{\{state\}\}">S</figure-callout>}}_b\&CenterDot;S_{a0})}<0.10---\left(10\right)$

Wherein, Sa and Sb are the length of any luminous point of scanning ray formation on the photosensitive drums 15 at Y direction and directions X, δ is the ratio of smallest spot and maximum luminous point on the photosensitive drums 15, and η is the ratio of luminous point on the luminous point of scanning ray on mems mirror 10 reflectings surface and the photosensitive drums 15; S _A0With S _B0Be the luminous point of scanning ray on mems mirror 10 reflectings surface length at main scanning direction and sub scanning direction.

For making the present invention clear and definite more full and accurate, enumerate preferred embodiment and cooperate following diagram, details are as follows with structure of the present invention and technical characterictic thereof:

The following embodiment that is disclosed of the present invention, be at the main composition assembly of the two-chip type f theta lens of MEMS laser scanning device of the present invention and explain, though therefore the following embodiment that is disclosed of the present invention is applied in the MEMS laser scanning device, but with regard to generally having MEMS laser scanning device, except disclosed two-chip type f theta lens, other structure belongs to known technology, therefore it will be understood by a person skilled in the art that, the constituent components of the two-chip type f theta lens of disclosed MEMS laser scanning device is not limited to the following example structure that discloses, just each constituent components of the two-chip type f theta lens of this MEMS laser scanning device is to carry out many changes, revise, even the equivalence change, for example: the radius-of-curvature design of first eyeglass 131 and second eyeglass 132 or the design of face type, material is selected for use, spacing adjustment etc. is not limited.

＜the first embodiment 〉

Consult Fig. 3 and Fig. 6, wherein Fig. 6 is the optical path figure of the embodiment of the present invention's scanning ray of passing through first eyeglass and second eyeglass.First eyeglass 131 of the two-chip type f theta lens of present embodiment and one second eyeglass 132, wherein the first eyeglass 131a is lenticular eyeglass, wherein second eyeglass 132 is constituted by a double concave eyeglass, the 3rd optical surface 132a and the 4th optical surface 132b of the first optical surface 131a of first eyeglass 131 and the second optical surface 131b, second eyeglass 132 are aspheric surface, use formula (2) to be the aspheric surface formulae design.Its optical characteristics and aspheric surface parameter such as table one and table two.

The f θ optical characteristics of table one, first embodiment

Optical surface (optical surface)	Radius-of-curvature (mm) (curvature)	D thickness (mm) (thickness)	n dRefractive index (refraction index)
				MEMS reflecting surface R0	0.00	26.23	1
Eyeglass 1 (lens 1)			1.491757
				R1 (horizontal picture curved surface)
R1x*	-123.97	15.00
				R1y*	275.33
R2 (horizontal picture curved surface)
				R2x*	-30.25	11.45
R2y*	-39.80
				Eyeglass 2 (lens 2)			1.491757
R3 (horizontal picture curved surface)
				R3x*	36.03	8.53
R3y*	-127.80
				R4 (horizontal picture curved surface)
R4x*	-92.40	109.50
				R4y*	82.47
Photosensitive drums (drum) R5	0.00	0.00
				* represent aspheric surface

The optical surface aspheric surface parameter of table two, first embodiment

Two-chip type f theta lens through being constituted thus, f _{(1) Y}=67.05, f _{(2) Y}=-93.76, f _SX=32.257, f _SY=147 (mm) can convert scanning ray to distance and be linear scanning ray luminous point with the time, and with luminous point S on the mems mirror 10 _A0=19.434 (μ m), S _B0=3972.24 (μ m) scanning becomes scanning ray, in photosensitive drums 15 enterprising line focusings, forms less luminous point 6, and satisfies the condition of formula (4)～formula (10), as table three; On the photosensitive drums with the Gaussian beam diameter (μ m) of central shaft Z axle, as table four at the luminous point of Y direction distance center axle Y distance (mm); And the luminous point distribution plan of present embodiment as shown in Figure 7.Among the figure, the unit circle diameter is 0.05mm.

Table three, first embodiment table that satisfies condition

The maximal value of luminous point Gaussian beam diameter on table four, the first embodiment photosensitive drums

?Y	-107.500	-98.223	-89.648	-71.924	-53.905	-35.870	-17.906	0.000
									?Max(2Ga，2Gb)	4.42E-03	3.42E-03	4.84E-03	4.79E-03	4.41E-03	4.12E-03	3.39E-03	2.66E-03

＜the second embodiment 〉

First eyeglass 131 of the two-chip type f theta lens of present embodiment and one second eyeglass 132, wherein first eyeglass 131 is lenticular eyeglass, wherein second eyeglass 132 is constituted by a double concave eyeglass, the 3rd optical surface 132a of the first optical surface 131a of first eyeglass 131 and the second optical surface 131b, second eyeglass 132, the 4th optical surface 132b of second eyeglass 132 are aspheric surface, use formula (2) to be the aspheric surface formulae design.Its optical characteristics and aspheric surface parameter such as table five and table six.

The f θ optical characteristics of table five, second embodiment

Optical surface (optical surface)	Radius-of-curvature (mm) (curvature)	D thickness (mm) (thickness)	n dRefractive index (refraction index)
				MEMS reflecting surface R0	0.00	18.58	1
Eyeglass 1 (lens 1)			1.491757
				R1 (horizontal picture curved surface)
R1x*	235.60	15.00
				R1y*	-1411.53
R2 (horizontal picture curved surface)
				R2x*	-29.04	9.25
R2y*	-31.08
				Eyeglass 2 (lens 2)			1.491757
R3 (horizontal picture curved surface)
				R3x*	32.84	11.55
R3y*	-101.85
				R4 (horizontal picture curved surface)
R4x*	-73.84	110.20
				R4y*	-7.53
Photosensitive drums (drum) R5	0.00	0.00

* represent aspheric surface

The optical surface aspheric surface parameter of table six, second embodiment

Two-chip type f theta lens through being constituted thus, f _{(1) Y}=60.299, f _{(2) Y}=-80.169, f _SX=27.399, f _SY=145.725 (mm) can convert scanning ray to distance and be linear scanning ray luminous point with the time, and with luminous point S on the mems mirror 10 _A0=19.434 (μ m), S _B0=3972.24 (μ m) scanning becomes scanning ray, in photosensitive drums 15 enterprising line focusings, forms less luminous point 8, and satisfies the condition of (4)～formula (10), as table seven; On the photosensitive drums 15 with the Gaussian beam diameter (μ m) of central shaft Z axle, as table eight at the luminous point of Y direction distance center axle Y distance (mm); And the luminous point distribution plan of present embodiment as shown in Figure 8.Among the figure, the unit circle diameter is 0.05mm.

Table seven, second embodiment table that satisfies condition

The maximal value of luminous point Gaussian beam diameter on table eight, the second embodiment photosensitive drums

?Y	-107.545	-98.226	-89.602	-71.765	-53.660	-35.621	-17.750	0.000
									?Max(2Ga，2Gb)	1.40E-02	1.49E-02	1.99E-02	3.27E-03	9.30E-03	2.04E-02	2.15E-02	8.17E-03

＜the three embodiment 〉

First eyeglass 131 of the two-chip type f theta lens of present embodiment and one second eyeglass 132, wherein first eyeglass 131 is lenticular eyeglass, wherein second eyeglass 132 is constituted by a double concave eyeglass, the 3rd optical surface 132a of the first optical surface 131a of first eyeglass 131 and the second optical surface 131b, second eyeglass 132, the 4th optical surface 132b of second eyeglass 132 are aspheric surface, use formula (2) to be the aspheric surface formulae design.Its optical characteristics and aspheric surface parameter such as table nine and table ten.

The f θ optical characteristics of table nine, the 3rd embodiment

Optical surface (optical surface)	Radius-of-curvature (mm) (curvature)	D thickness (mm) (thickness)	n dRefractive index (refraction index)
				MEMS reflecting surface R0	0.00	25.30	1
Eyeglass 1 (lens 1)			1.527
				R1 (horizontal picture curved surface)
R1x*	-129.15	12.84
				R1y*	307.34
R2 (horizontal picture curved surface)
				R2x*	-29.48	12.63
R2y*	-39.22
				Eyeglass 2 (lens 2)			1.527
R3 (horizontal picture curved surface)
				R3x*	34.60	6.80
R3y*	-128.29
				R4 (horizontal picture curved surface)
R4x*	-91.52	108.56
				R4y*	80.87
Photosensitive drums (drum) R5	0.00	0.00

* represent aspheric surface

The optical surface aspheric surface parameter of table ten, the 3rd embodiment

Two-chip type f theta lens through being constituted thus, f _{(1) Y}=66.828, f _{(2) Y}=-93.029, f _SX=31.634, f _SY=146.296 (mm) can convert scanning ray to distance and be linear scanning ray luminous point with the time, and with luminous point S on the mems mirror 10 _A0=19.434 (μ m), S _B0=3972.24 (μ m) scanning becomes scanning ray, in photosensitive drums 15 enterprising line focusings, forms less luminous point 10, and satisfies the condition of (4)～formula (10), as table ten one; On the photosensitive drums with the Gaussian beam diameter (μ m) of central shaft Z axle, as table ten two at the luminous point of Y direction distance center axle Y distance (mm); The luminous point distribution plan of present embodiment as shown in Figure 9.Among the figure, the unit circle diameter is 0.05mm.

Table ten the one, the 3rd embodiment table that satisfies condition

The maximal value of luminous point Gaussian beam diameter on table ten the two, the 3rd embodiment photosensitive drums

?Y	-108.012	-98.457	-89.700	-71.761	-53.680	-35.677	-17.799	0.000
									?Max(2Ga，2Gb)	5.57E-03	7.53E-03	1.01E-02	1.39E-02	1.27E-02	6.20E-03	7.21E-03	7.90E-03

＜the four embodiment 〉

First eyeglass 131 of the two-chip type f theta lens of present embodiment and one second eyeglass 132, wherein first eyeglass 131 is lenticular eyeglass, wherein second eyeglass 132 is constituted by a double concave eyeglass, the 3rd optical surface 132a of the first optical surface 131a of first eyeglass 131 and the second optical surface 131b, second eyeglass 132 is an aspheric surface, uses formula (2) to be the aspheric surface formulae design; The 4th optical surface 132b uses formula (3) to be the aspheric surface formulae design at second eyeglass 132.Its optical characteristics and aspheric surface parameter such as table ten three and table ten four.

The f θ optical characteristics of table ten the three, the 4th embodiment

Optical surface (optical surface)	Radius-of-curvature (mm) (curvature)	D thickness (mm) (thickness)	n dRefractive index (refraction index)
				MEMS reflecting surface R0	0.00	27.07	1
Eyeglass 1 (lens 1)			1.52528
				R1 (horizontal picture curved surface)
R1x*	-124.92	15.00
				R1y*	268.85
R2 (horizontal picture curved surface)
				R2x*	-30.37	11.92
R2y*	-39.70
				Eyeglass 2 (lens 2)			1.52528
R3 (horizontal picture curved surface)
				R3x*	36.01	8.00
R3y*	-124.55
				R4 (Y encircles as curved surface)
R4x	-93.35	110.02
				R4y*	83.27
Photosensitive drums (drum) R5	0.00	0.00

* represent aspheric surface

The optical surface aspheric surface parameter of table ten the four, the 4th embodiment

Two-chip type f theta lens through being constituted thus, f _{(1) Y}=67.743, f _{(2) Y}=-94.854, f _SX=32.864, f _SY=147.91 (mm) can convert scanning ray to distance and be linear scanning ray luminous point with the time, and with luminous point S on the mems mirror 10 _A0=19.434 (μ m), S _B0=3972.24 (μ m) scanning becomes scanning ray, in photosensitive drums 15 enterprising line focusings, forms less luminous point 12, and satisfies the condition of (4)～formula (10), as table ten five; On the photosensitive drums with the Gaussian beam diameter (μ m) of central shaft Z axle, as table ten six at the luminous point of Y direction distance center axle Y distance (mm); And the luminous point distribution plan of present embodiment as shown in figure 10.Among the figure, the unit circle diameter is 0.05mm.

Table ten the five, the 4th embodiment table that satisfies condition

The maximal value of luminous point Gaussian beam diameter on table ten the six, the 4th embodiment photosensitive drums

?Y	-107.545	-98.226	-89.602	-71.765	-53.660	-35.621	-17.750	0.000
									?Max(2Ga，2Gb)	4.58E-03	3.66E-03	4.84E-03	4.59E-03	3.16E-03	3.62E-03	3.32E-03	2.50E-03

By the above embodiments explanation, the present invention can reach following effect at least:

(1) setting by two-chip type f theta lens of the present invention, the speed scanning phenomenon such as non-that the mems mirror that is simple harmonic motion can be successively decreased by increasing in time originally or increases progressively at imaging surface glazing dot spacing, speed scanning such as be modified to, make speed such as the projection work scanning of laser beam, the spacing that images in the two adjacent luminous points that form on the object is equated at imaging surface.

(2) setting by two-chip type f theta lens of the present invention can be dwindled the luminous point on the object that focuses on imaging to the correction that distorts at main scanning direction and sub scanning direction scanning ray.

(3) setting by two-chip type f theta lens of the present invention can make the luminous point size homogenising that is imaged on the object to the correction that distorts at main scanning direction and sub scanning direction scanning ray.

The above only is the preferred embodiments of the present invention, only is illustrative for the purpose of the present invention, and nonrestrictive; It will be understood by those skilled in the art that in the spirit and scope that limit in claim of the present invention and can carry out many changes, revise it, even the equivalence change, but all will fall within the scope of protection of the present invention.

Claims (4)

1. the two-chip type f theta lens of a MEMS laser scanning device, it is applicable to a 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; This two-chip type f theta lens comprises, start in regular turn by this mems mirror, constituted by lenticular first eyeglass and second eyeglass of a double concave, 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, with the scanning ray luminous point of the angle of this mems mirror reflection and time nonlinear relationship convert to apart from the time be the scanning ray luminous point of linear relationship; Wherein this second eyeglass has one the 3rd optical surface and one the 4th optical surface, and 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, and the scanning ray correction of this first eyeglass is concentrated on this object; By of scanning ray on this object the imaging of this two-chip type f theta lens with this mems mirror reflection,

Wherein, further satisfy following condition at main scanning direction:

$1.6<\frac{d_3+d_4+d_5}{f_{\left(1\right)Y}}<2.5;$

$-2.0<\frac{d_5}{f_{\left(2\right)Y}}<-1.0,$

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

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

Satisfy at main scanning direction $0.2<|f_{\mathrm{sY}}\&CenterDot;(\frac{(n_{d1}-1)}{f_{\left(1\right)y}}+\frac{(n_{d2}-1)}{f_{\left(2\right)y}})|<0.4,$

Satisfy at sub scanning direction $0.8<|(\frac{1}{R_{1x}}-\frac{1}{R_{2x}})+(\frac{1}{R_{3x}}-\frac{1}{R_{4x}})f_{\mathrm{sX}}|<1.6$

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

3. 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, S _aWith S _bBe respectively any luminous point that scanning ray on this object forms length at main scanning direction and sub scanning direction, δ is the ratio of smallest spot and maximum luminous point on this object.

4. the two-chip type f theta lens of MEMS laser scanning device as claimed in claim 1, wherein the ratio of the ratio of maximum luminous point and smallest spot on this object satisfies respectively 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 respectively the length of the luminous point of scanning ray on this mems mirror reflecting surface, S at main scanning direction and sub scanning direction _aWith S _bBe respectively the length of any luminous point of scanning ray formation on this object, η 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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