A laser scanning system

Abstract

The present invention relates to the field of laser scanning technology, and discloses a laser scanning system, comprising: a light source for outputting laser light; a DOE free-form surface lens disposed on the outgoing light path of the laser for shaping the laser light; a polygonal mirror for reflecting the shaped laser light at different angles; an F-lens group for converging the laser light reflected at different angles; wherein the F-lens group includes a first lens and a second lens, the first lens is used for correcting the reflected laser light, and the second lens is used for converging the corrected laser light. By designing a DOE free-form surface lens to shape the laser light and combining it with a mirror and an F-lens group, the present invention achieves high-precision and uniform scanning of the scanned image, reduces optical distortion and improves optical efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of laser scanning, and particularly to a laser scanning system. Background Art

[0002] A scanning system is a key component in a scanning device, responsible for capturing and processing images or data of the object being scanned. Scanning devices can be applied in various fields such as office automation, logistics management, medical imaging, etc. The performance of the scanning system directly affects the overall performance of the scanning device, including scanning speed, clarity, etc.

[0003] The principle of the scanning system is as follows: The light source illuminates the surface of the target object, and the light is reflected or transmitted through the target object for scanning. For the scanned light, a photosensitive element or an image sensor can be used to convert the optical signal into an electrical signal for subsequent processing and storage.

[0004] In the existing scanning systems, when collimating and shaping the laser, the commonly used collimation and shaping scheme requires the combined use of a cylindrical lens and an aspherical lens, with high requirements for assembly and fitting accuracy, and a relatively large change in the distance between points during the scanning process, resulting in poor uniformity of the image.

[0005] Therefore, there is an urgent need to develop a laser scanning system to solve the above problems. Summary of the Invention

[0006] To solve the above technical problems, the present invention provides a laser scanning system, which shapes the laser by designing a DOE free-form lens and combines it with a reflecting mirror and an F- lens group to achieve high-precision and uniform scanning of the scanned image.

[0007] The present invention provides a laser scanning system, comprising:

[0008] A light source for outputting laser light;

[0009] A DOE free-form lens disposed on the output light path of the laser for shaping the laser; a diffraction structure is provided on the first optical surface of the DOE free-form lens close to the light source side;

[0010] A multi-faceted reflecting mirror for reflecting the shaped laser at different angles;

[0011] An F- lens group for converging the laser reflected at different angles;

[0012] Wherein, the F- lens group includes a first lens and a second lens. The first lens is used to correct the reflected laser, and the second lens is used to converge the corrected laser.

[0013] Further, the focal length of the F-lens group in the x direction is 210 ± 10 mm, and the focal length in the y direction is 40 ± 10 mm.

[0014] Further, the side of the DOE free-form surface lens close to the polyhedral mirror is the second optical surface;

[0015] The first optical surface is a 16th-order first polynomial formula, and the first polynomial does not include odd-order terms;

[0016] The second optical surface is a 16th-order second polynomial formula.

[0017] Further, a Cartesian rectangular coordinate system O'-x'y'z' is established with the vertices of the first optical surface and the second optical surface as the origin O';

[0018] Based on the O'-x'y'z' coordinate system, the first polynomial formula is:

[0019] ,

[0020] where is the polar radius, c is the surface curvature, k is the conic coefficient, , , , , , , , are the aspheric coefficients corresponding to the polar radii of different orders respectively;

[0021] The second polynomial formula is:

[0022] ,

[0023] where is the surface curvature in the x' direction, is the radius of curvature in the x' direction, is the surface curvature in the y' direction, is the radius of curvature in the x' direction, k x is the conic coefficient in the x' direction, k y is the conic coefficient in the y' direction; is the aspheric coefficient in the x' direction, is the aspheric coefficient in the y' direction, and m and n are the orders in the x' direction and the y' direction respectively.

[0024] Further, based on the O'-x'y'z' coordinate system of the first optical surface, the diffraction structure equation is:

[0025] ,

[0026] Wherein, is the optical path, M is the diffraction order, N is the order, is the diffraction aspheric coefficient at the i-th order.

[0027] Further, one side of the first lens close to the polyhedral mirror is the third optical surface, one side of the first lens close to the second lens is the fourth optical surface, one side of the second lens close to the first lens is the fifth optical surface, and one side of the second lens away from the first lens is the sixth optical surface;

[0028] An O-xyz coordinate system is respectively constructed with the vertex O of each optical surface of the first lens and the second lens as the coordinate origin;

[0029] The surface expressions of the third optical surface and the first optical surface in different coordinate systems are the same;

[0030] The surface expressions of the second optical surface and the fifth optical surface in different coordinate systems are the same;

[0031] The surface expressions of the fourth optical surface and the sixth optical surface in different coordinate systems are the same.

[0032] Further, based on the O-xyz coordinate system, the surface expression of the fourth optical surface or the sixth optical surface is:

[0033] ,

[0034] Wherein, are the coefficients corresponding to different orders of y respectively; is the surface curvature in the y direction, is the vertex curvature in the y direction, K y is the conic coefficient in the y direction, represents the vertex curvature in the x direction;

[0035] , wherein, are the aspheric coefficients corresponding to different orders of y in the x direction respectively, and R is the radius of curvature.

[0036] The embodiments of the present invention have the following technical effects:

[0037] In this application, a DOE free-form lens is designed to shape the laser, and a diffraction structure is designed on the first optical surface to improve the reflectivity of the lens and reduce the light loss. When used in combination with a mirror and an F- lens group, wherein by the F- Each optical surface of the lens group is designed to achieve high-precision and uniform scanning of the scanned image, reduce optical distortion and improve optical efficiency. Description of the Drawings

[0038] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0039] Figure 1 is a schematic structural diagram of a laser scanning system provided by an embodiment of the present invention;

[0040] Figure 2 is a schematic diagram showing the relationship between the magnification and the scanning frame width provided by Embodiment 2 of the present invention;

[0041] Figure 3 is a spot diagram provided by Embodiment 2 of the present invention;

[0042] Figure 4 is an energy distribution diagram provided by Embodiment 2 of the present invention.

[0043] In the figure, 1 is a light source; 2 is a DOE free-form surface lens; 3 is a polygonal mirror; 4 is an F- lens group; 5 is a first lens; 6 is a second lens. Detailed Embodiments

[0044] To make the objectives, technical solutions and advantages of the present invention clearer, the following will clearly and completely describe the technical solutions of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention. Embodiment 1

[0045] Figure 1 is a schematic structural diagram of a laser scanning system provided by an embodiment of the present invention. Refer to Figure 1 , specifically including:

[0046] A light source 1 for outputting laser light; emitting single-wavelength Gaussian light with a wavelength between 700 and 800 mm.

[0047] A DOE free-form surface lens 2 is arranged on the outgoing light path of the laser for shaping the laser; so that the light beam is accurately irradiated into a specific shape requirement and the energy distribution of the light beam is adjusted to make its distribution more uniform;

[0048] A multi-faceted mirror 3 for reflecting the shaped laser at different angles; enabling the light beam to be scanned along a predetermined path;

[0049] F- A lens group 4 for converging the laser reflected at different angles; to control the diameter of the light beam so as to ensure the width and precision of the line, correct aberration, etc.

[0050] Among them, the said F- The lens group 4 includes a first lens 5 and a second lens 6. The first lens 5 is used to correct the reflected laser, and the second lens 6 is used to converge the corrected laser.

[0051] F- The focal length of the lens group 4 in the x direction is 210 10 mm, and the focal length in the y direction is 40 10 mm, further defining the focal length range to ensure the imaging quality in two different directions.

[0052] One side of the DOE free-form lens 2 close to the multi-faceted mirror 3 is the second optical surface;

[0053] The first optical surface is a 16th-order first polynomial formula that does not include odd-order terms; the second optical surface is a 16th-order second polynomial formula.

[0054] The DOE free-form lens 2 respectively establishes a Cartesian rectangular coordinate system O’-x’y’z’ with the vertices of the first optical surface and the second optical surface as the origin O’;

[0055] Based on the O’-x’y’z’ coordinate system, the first polynomial formula is:

[0056] ,

[0057] Among them, is the polar radius, c is the surface curvature, k is the conic coefficient, , , , , , , , are the aspherical coefficients corresponding to the polar radii of different orders respectively.

[0058] Based on the O’-x’y’z’ coordinate system of the first optical surface, the diffraction structure equation is:

[0059] ,

[0060] Among them, is the optical path, M is the diffraction order, N is the order, is the diffraction aspheric coefficient at the i-th order.

[0061] The design of the first optical surface adds a diffraction structure on the basis of the aspheric surface. Coating the optical coating on the first optical surface composed of the first polynomial formula is equivalent to the superposition of two aspheric surfaces to shorten the focal length, improve the reflectivity of the lens and reduce light loss.

[0062] Based on the O’-x’y’z’ coordinate system, the second polynomial formula is:

[0063] ,

[0064] where, is the surface curvature in the x’ direction, is the radius of curvature in the x’ direction, is the surface curvature in the y’ direction, is the radius of curvature in the x’ direction, k x is the conic coefficient in the x’ direction, k y is the conic coefficient in the y’ direction; is the aspheric coefficient in the x’ direction, is the aspheric coefficient in the y’ direction, m and n are the orders in the x’ direction and the y’ direction respectively.

[0065] The second optical surface is a freeform surface with non-rotational symmetry. This design makes the curvatures in the x and y directions different. Therefore, the fast and slow axes of the laser can be compressed separately to achieve a better compression effect.

[0066] One side of the first lens 5 close to the polygonal mirror 3 is the third optical surface, one side of the first lens 5 close to the second lens 6 is the fourth optical surface, one side of the second lens 6 close to the first lens 5 is the fifth optical surface, and one side of the second lens 6 far from the first lens 5 is the sixth optical surface;

[0067] Taking the vertex O of each optical surface of the first lens 5 and the second lens 6 as the coordinate origin respectively to construct the O-xyz coordinate system; where:

[0068] The surface expressions of the third optical surface and the first optical surface in different coordinate systems are the same;

[0069] Based on the O-xyz, the surface expression corresponding to the third optical surface is:

[0070] ,

[0071] where, is the polar radius, c’ is the surface curvature, k’ is the conic coefficient, , , , , , , , are the aspherical coefficients corresponding to different orders of the polar radius respectively;

[0072] (2) The surface expressions of the second optical surface and the fifth optical surface are the same in different coordinate systems;

[0073] Based on O-xyz, the surface expression corresponding to the fifth optical surface is:

[0074] ,

[0075] where is the surface curvature in the x direction, is the radius of curvature in the x direction, is the surface curvature in the y direction, is the radius of curvature in the x direction, k x ’ is the conic coefficient in the x direction, k y ’ is the conic coefficient in the y direction; is the aspherical coefficient in the x direction, is the aspherical coefficient in the y direction, m’ and n’ are the orders in the x direction and the y direction respectively.

[0076] (3) The surface expressions of the fourth optical surface and the sixth optical surface are the same in different coordinate systems.

[0077] Based on the O-xyz coordinate system, the surface expression of the fourth optical surface or the sixth optical surface is:

[0078] ,

[0079] where are the coefficients corresponding to different orders of y respectively; is the surface curvature in the y direction, is the vertex curvature in the y direction, K y is the conic coefficient in the y direction, represents the vertex curvature in the x direction;

[0080] , where are the aspherical coefficients corresponding to different orders of x and y respectively, and R is the radius of curvature.

[0081] The settings of the fourth optical surface and the sixth optical surface make the smoothness of the corresponding surface smoother, easier to process, and beneficial to the formation of the surface profile.

[0082] Based on the above settings, the following explanations are made:

[0083] The laser beam shaped by the DOE free-form lens 2 forms a linear light spot on the polygonal mirror 3, and the width of the line is less than 0.5 mm.

[0084] The function of the polygonal mirror 3 is to reflect the shaped light beam into the F- lens group 4. The polygonal mirror 3 rotates driven by a high-speed motor. The reflection angles are different at different rotation angles. Therefore, when the light beam is reflected by the rotating polygonal mirror 3, multi-angle scanning is achieved.

[0085] Specifically, the motor speed is limited within the range of 20000 RPM to 50000 RPM. The dynamic scanning balance is less than 0.05% P-P. The flatness of each surface of the polygonal mirror 3 is less than 0.6 μm, and the tower difference is less than 300.

[0086] The laser beam reflected by the polygonal mirror 3 enters the F- lens group 4 at different angles. The main contribution of the first lens 5 is to correct distortion. After the light beam passes through the third optical surface of the first lens 5, the light beam angle expands, increasing the scanning angle. The third optical surface is a concave aspherical surface, which plays a role in correcting distortion. The light beam is first converged through the fourth optical surface of the lens 5. The fourth optical surface is a free-form surface, and the ratio of the optical power in the X direction to that in the Y direction is greater than 1 / 20, correcting the spherical aberration in the X and Y directions.

[0087] The main function of the second lens 6 is to converge the light spot. The light beam passes through the fifth optical surface of the second lens 6 to correct the field curvature in the Y direction and expand the depth of field. The fourth optical surface is a free-form surface, which converges the light beam in the X direction and corrects the field curvature in the Y direction.

[0088] The light beam passes through the sixth optical surface to further correct the F- distortion in the Y direction. Finally, the F- distortion is less than 0.1%. The light spot is converged in the X direction, so that the final convergence point in the X direction is at the same position as the light spot convergence point in the Y direction, and finally a uniform light spot distribution is presented on the imaging surface.

[0089] In summary, the combination of the first lens 5 and the second lens 6 converges the reflected laser beam into a circular light spot. The difference in the size of the light spots at different positions is less than 5 μm, and each light spot position is evenly distributed, that is, the F- distortion is less than 0.1%.

[0090] Based on the above technical solution, after the light source 1 emits a laser beam, it is collimated and shaped by the DOE free-form lens 2, and a line light spot is presented on the polygonal mirror 3 with a line width less than 0.5 mm. Then it is reflected by the polygonal mirror and reaches the F- lens group, and the F- The lens group converges light rays, and finally converges them onto the scanning surface to form a circular light spot. Embodiment 2

[0091] Based on the content of Embodiment 1, this application provides a specific implementation:

[0092] Specific values are set for the diffraction structure and each surface. Refer to Tables 1 to 6;

[0093] Table 1 Parameter Settings of the First Optical Surface and Diffraction Structure

[0094] numerical value 1 / c 22.00027014 k -10.96701214 <![CDATA[α2]]> 0 <![CDATA[α4]]> 0 <![CDATA[α6]]> 0 <![CDATA[α8]]> 0 <![CDATA[α 10 > 0 <![CDATA[P2]]> 82.27890350 <![CDATA[P4]]> 0.53546872 <![CDATA[P6]]> 0.00269054

[0095] Table 2 Parameter Settings of the Second Optical Surface

[0096] numerical value <![CDATA[r y > -1.281950809E+01 <![CDATA[k y > 0.000000000E+00 <![CDATA[r x > -1.043357764E+01 <![CDATA[k x > 3.197154740E+02 <![CDATA[β1]]> 0.0000000E+00 <![CDATA[β2]]> 0.0000000E+00 <![CDATA[β3]]> 0.0000000E+00 <![CDATA[β4]]> 0.0000000E+00 <![CDATA[β5]]> 0.0000000E+00 <![CDATA[β6]]> 0.0000000E+00 <![CDATA[β7]]> 0.0000000E+00 <![CDATA[β8]]> 0.0000000E+00 <![CDATA[γ1]]> 2.7033694E-14 <![CDATA[γ2]]> -1.1811041E-10 <![CDATA[γ3]]> 7.9951704E-11 <![CDATA[γ4]]> -1.1811041E-10 <![CDATA[γ5]]> 7.9951704E-11 <![CDATA[γ6]]> 0.0000000E+00 <![CDATA[γ7]]> 0.0000000E+00 <![CDATA[γ8]]> 0.0000000E+00 <![CDATA[γ9]]> 0.0000000E+00

[0097] Table 3 Curved Surface Parameter Settings of the Third Optical Surface

[0098] numerical value 1 / c 5.327778E+01 k -1.096701E+01 <![CDATA[α1]]> 0.000000E+00 <![CDATA[α2]]> 5.895536E-07 <![CDATA[α3]]> -7.450482E-10 <![CDATA[α4]]> -4.621565E-13 <![CDATA[α5]]> 1.177703E-17 <![CDATA[α6]]> 0 <![CDATA[α7]]> 0 <![CDATA[α8]]> 0

[0099] Table 4 Parameter Settings of the Fourth Optical Surface

[0100] numerical value R inf <![CDATA[C x > -3.1742084075E-02 <![CDATA[C y > 2.8388115263E-02 <![CDATA[K x > 0.0000000000E+00 <![CDATA[K y > -1.2987564069E+00 <![CDATA[A n > -2.809541013E-06 <![CDATA[B n > 1.034861757E-09 <![CDATA[C n > 1.134526037E-13 <![CDATA[D n > -6.895849935E-16 <![CDATA[E n > 0.000000000E+00 <![CDATA[F n > 0.000000000E+00 <![CDATA[a n > -1.0900061478E-04 <![CDATA[b n > 4.7744010498E-06 <![CDATA[c n > -2.7176110394E-07 <![CDATA[d n > 1.2507867022E-07 <![CDATA[e n > 1.1120921632E-09 <![CDATA[f n > -1.0492783809E-10 <![CDATA[j n > -8.9978494997E-13

[0101] Table 5 Parameter Settings of the Fifth Optical Surface

[0102] numerical value <![CDATA[r y > 1.7746108E+02 <![CDATA[k y > 0.0000000E+00 <![CDATA[r x > 3.4354594E+03 <![CDATA[k x > 3.1971547E+02 <![CDATA[β1]]> 0.0000000E+00 <![CDATA[β2]]> -7.3888732E-03 <![CDATA[β3]]> 0.0000000E+00 <![CDATA[β4]]> 1.6571395E-05 <![CDATA[β5]]> 0.0000000E+00 <![CDATA[β6]]> -3.7344608E-07 <![CDATA[β7]]> 0.0000000E+00 <![CDATA[β8]]> -4.9185599E-08 <![CDATA[γ1]]> -1.3744418E-03 <![CDATA[γ2]]> 2.7216854E-07 <![CDATA[γ3]]> -5.2507877E-07 <![CDATA[γ4]]> -1.1811041E-10 <![CDATA[γ5]]> 7.9951704E-11 <![CDATA[γ6]]> 2.7033694E-14 <![CDATA[γ7]]> -2.4016548E-15 <![CDATA[γ8]]> -2.3763260E-18 <![CDATA[γ9]]> -4.8276534E-19

[0103] Table 6 Parameter Settings of the Sixth Optical Surface

[0104] numerical value R inf <![CDATA[C x > 4.006130900E-06 <![CDATA[C y > -4.120813900E-06 <![CDATA[K x > -9.181756600E-10 <![CDATA[K y > 3.956387700E-10 <![CDATA[A n > 3.830322700E-07 <![CDATA[B n > -1.114284800E-10 <![CDATA[C n > 2.355219200E-14 <![CDATA[D n > -2.238117700E-18 <![CDATA[E n > 5.383609000E-23 <![CDATA[F n > 0.000000000E+00 <![CDATA[a n > -1.0900061478E-04 <![CDATA[b n > 4.7744010498E-06 <![CDATA[c n > -2.7176110394E-07 <![CDATA[d n > 1.2507867022E-07 <![CDATA[e n > 1.1120921632E-09 <![CDATA[f n > -1.0492783809E-10 <![CDATA[j n > -8.9978494997E-13

[0105] Among them, inf in the table represents infinity. Based on the above parameter settings, relevant experimental verifications were carried out:

[0106] Figure 2 The abscissa represents the width of the scanning frame, the ordinate is the magnification, the absolute value is the change in magnification corresponding to the width of every 10 mm of the scanning frame, and the relative value is the change in magnification of every 10 mm of the scanning frame relative to the magnification of the entire frame. Obviously, it can be seen from the figure that the magnification is less than 0.2%.

[0107] Figure 3 The circle in the middle is the diffraction limit, and the size of the imaging converging light spot is shown in the middle of the circle. The smaller the converging light spot, the higher the resolution of the imaging picture. The defocus position is the defocus range. 2 mm is a relatively large defocus range. The larger the defocus position, the fact that the light spot is still within the diffraction limit indicates that the tolerance of the system of this application is better.

[0108] Figure 4 The abscissa represents the scanning frame width, and the ordinate represents the energy distribution. It can be seen that the energy uniformity is greater than 95%.

[0109] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the embodiments of the present invention.

Claims

1. A laser scanning system, characterized in that: include: A light source (1) for outputting laser light; A DOE free-form surface lens (2) is arranged on an exit optical path of the laser and is used to shape the laser; a diffraction structure is provided on a first optical surface of the DOE free-form surface lens (2) on a side close to the light source (1); The first optical surface is a 16th-order first polynomial formula, and the first polynomial does not include odd-order terms; Establish a Cartesian rectangular coordinate system O'-x'y'z' with the vertices of the first optical surface and the second optical surface as the origin O'; Based on the O'-x'y'z' coordinate system, the first polynomial formula is: ， in, is the polar diameter, c is the surface curvature, k is the cone coefficient, , , , , , , , They are the aspheric coefficients corresponding to different order polar diameters; The side of the DOE free-form surface lens (2) close to the multi-faceted reflector (3) is a second optical surface; The second optical surface is a second polynomial formula of degree 16; A multi-faceted reflector (3) is used to reflect the shaped laser light at different angles; F- A lens group (4) is used to converge laser beams reflected at different angles; Among them, the F- The lens group (4) comprises a first lens (5) and a second lens (6), wherein the first lens (5) is used to correct the reflected laser light, and the second lens (6) is used to converge the corrected laser light.

2. A laser scanning system according to claim 1, characterized in that: The F- The focal length of lens group (4) in the x direction is 210 10mm, focal length in y direction is 40 10mm.

3. A laser scanning system according to claim 1, characterized in that: Establish a Cartesian rectangular coordinate system O'-x'y'z' with the vertices of the first optical surface and the second optical surface as the origin O'; Based on the O'-x'y'z' coordinate system, the second polynomial formula is: ， in, is the surface curvature in the x' direction, is the radius of curvature in the x' direction, is the surface curvature in the y' direction, is the radius of curvature in the x' direction, k x is the cone coefficient in the x' direction, k y is the cone coefficient in the y' direction; is the aspheric coefficient in the x' direction, is the aspheric coefficient in the y' direction, m and n are the order in the x' and y' directions respectively.

4. A laser scanning system according to claim 3, characterized in that: Based on the O'-x'y'z' coordinate system of the first optical surface, the diffraction structure equation is: ， in, is the optical path, M is the diffraction pole, N is the order, is the diffraction aspheric coefficient of the i-th order.

5. A laser scanning system according to claim 3, characterized in that: The side of the first lens (5) close to the multi-faceted reflector (3) is a third optical surface, the side of the first lens (5) close to the second lens (6) is a fourth optical surface, the side of the second lens (6) close to the first lens (5) is a fifth optical surface, and the side of the second lens (6) far from the first lens (5) is a sixth optical surface; Constructing an O-xyz coordinate system using the vertices O of the optical surfaces of the first lens (5) and the second lens (6) as coordinate origins; The third optical surface and the first optical surface have the same surface expressions in different coordinate systems; The second optical surface and the fifth optical surface have the same surface expressions in different coordinate systems; The curved surface expressions of the fourth optical surface and the sixth optical surface in different coordinate systems are the same.

6. A laser scanning system according to claim 5, characterized in that: Based on the O-xyz coordinate system, the surface expression of the fourth optical surface or the sixth optical surface is: ， in, They are the coefficients corresponding to different orders of y; is the surface curvature in the y direction, is the vertex curvature in the y direction, K y is the cone coefficient in the y direction, represents the vertex curvature in the x direction; ,in, are the aspheric coefficients corresponding to different orders in the x-direction and y-direction, and R is the radius of curvature.

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