Coaxial focusing system for laser precision machining and installation method and focusing method

Abstract

The application provides a coaxial focusing system and mounting method and focusing method for laser precision machining, and the system comprises a projection imaging light path, a shooting taking light path and a laser focusing light path which are composed of a light source, a grating, a CCD, a half mirror, a lens, a full mirror, a half mirror, a laser system, a beam expander, a ceramic motor, an objective lens, a laser displacement sensor, a workpiece to be machined and a conjugate light path. The system is based on coaxial conjugate light path, combined with accurate measurement of the laser displacement sensor, overcomes the shortcomings of pure optical measurement and image comparison focusing method, realizes high-speed high-precision focusing and high-speed focus following function, and provides the best solution for laser machining of products with thickness deviation and surface deformation.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of laser precision machining, in particular to a coaxial focusing system for laser precision machining, and an installation method and a focusing method thereof. BACKGROUND

[0002] Focusing is an indispensable process for laser processing. Single machine and semi-automatic equipment often use manual focusing. In addition to low efficiency, the focusing accuracy is not enough due to individual differences of the operators, which affects the final machining accuracy. Common automatic optical focusing methods such as laser ranging and infrared ranging have high focusing efficiency, but are affected by the surface quality of the material, absorption, environmental temperature, etc., and the measurement value is prone to fluctuation. The image contrast focusing method has low efficiency.

[0003] High-precision semiconductor components such as wafer substrates require high processing efficiency and high sensitivity to focal length. The product needs to be in a closed dust-free environment, which is not suitable for manual focusing. In addition, different batches of products have thickness deviations, the product surface flatness is not good, and the product warps, which greatly affects the quality of laser processing. Therefore, it is necessary to develop a high-speed and high-precision automatic focusing system, and an automatic focal point following system that can automatically compensate for product thickness deviation and product warping. SUMMARY

[0004] The present application provides a coaxial focusing system for laser precision machining, and an installation method and a focusing method thereof, aiming to realize fast automatic optical focusing and real-time compensation of the laser focal point position according to the surface topography of the machined parts during high-speed processing, improve the adaptability of the laser processing equipment, and solve the problem of precise control of processing depth under the conditions of tilt and fluctuation of the vacuum adsorption platform of the laser processing equipment, uneven surface of the product to be processed, and product warping.

[0005] The first aspect of the application is a coaxial focusing system for laser precision machining, comprising: a light source (1), a grating (2), a first half mirror (4), a lens (5), a full mirror (6), a second half mirror (7), an objective lens (11), and a workpiece (13) arranged in sequence along the projection imaging light path, wherein the grating (2) diffracts the first parallel light beam (50) emitted by the LED light source (1) into a first divergent light beam (51), the first half mirror (4) reflects the first divergent light beam (51) into a second divergent light beam (52), the lens (5) converges the second divergent light beam (52) into a second parallel light beam (53), the full mirror (6) reflects the second parallel light beam (53) into a third parallel light beam (54), the second half mirror (7) reflects the third parallel light beam (54) into a fourth parallel light beam (55), and the objective lens (11) converges and projects the fourth parallel light beam (55) onto the workpiece (13); the lens (5) and the objective lens (11) form a pair of conjugate lenses, with focal points located at the grating (2) and the surface of the workpiece (13) respectively, and the grating (2) realizes projection imaging based on the principle of conjugate imaging on the workpiece (13);

[0006] The workpiece (13), the objective lens (11), the second half mirror (7), the full mirror (6), the lens (5), the first half mirror (4), a conjugate light path (14), and a CCD (3) are arranged in sequence along the shooting light path, wherein the workpiece (13) reflects the projection imaging into a first light beam (70), the objective lens (11) converges the first light beam (70) into a fifth parallel light beam (71), the second half mirror (7) reflects the fifth parallel light beam (71) into a sixth parallel light beam (72), the full mirror (6) reflects the sixth parallel light beam (72) into a seventh parallel light beam (73), the lens (5) converges the seventh parallel light beam (73) into a second light beam (74), the first half mirror (4) converges the second light beam (74) into a third light beam (75), the conjugate light path (14) first converges the third light beam (75) into an eighth parallel light beam (76), and then converges the eighth parallel light beam (76) into a fourth light beam (77), and the fourth light beam (77) is projected onto the CCD (3) to obtain the same magnified image as the grating (2), one of the focal points of the conjugate light path (14) is symmetric with the grating (2) with the first half mirror (4) as the symmetric axis, and the other focal point of the conjugate light path (14) is located on the photosensitive element of the CCD (3);

[0007] A laser system (8), a beam expander (9), a total reflection mirror (6), a second half mirror (7), an objective lens (11) and a workpiece (13) are arranged along a laser focusing light path in sequence, wherein the laser system (8) is used for emitting a laser beam (60), the beam expander (9) expands the laser beam (60) into a ninth parallel light beam (61), the ninth parallel light beam (61) is deflected by the total reflection mirror (6) and offset by the second half mirror (7) into a tenth parallel light beam (62), and the objective lens (11) focuses the tenth parallel light beam (62) on the workpiece (13).

[0008] The objective lens (11) is provided with a ceramic motor (10), and the ceramic motor (10) is arranged at a zero point.

[0009] The coaxial focusing system further comprises a laser displacement sensor (12) for measuring the relative distance between the workpiece (13) and the objective lens (11).

[0010] A further technical solution of the present application is that the light source (1) is an LED point light source or an LD laser light source.

[0011] A further technical solution of the present application is that when the light source (1) is an LED point light source, the focusing is realized by using a definition contrast method, specifically: according to the principle of conjugate light path imaging, when the grating (2) is projected most clearly on the surface of the workpiece (13), the surface of the workpiece (13) is just located at the focal point position of the objective lens (11), the entire focusing system is adjusted up and down, so that the CCD (3) obtains a clear image with the sharpest edge, and at this time, the projection position of the surface of the workpiece (13) is the focal point of the objective lens (11).

[0012] A further technical solution of the present application is that when the light source (1) is an LD laser light source, the focusing is realized by using a shape contrast method, specifically: the grating (2) is a semicircular structure, according to the principle of conjugate imaging, when the projection of the grating (2) is a semicircle on one side, the corresponding focal point is located below the surface of the workpiece (13), the focusing system needs to be adjusted upward, when the projection of the grating (2) is a semicircle on the other side, the corresponding focal point is located above the surface of the workpiece (13), the focusing system needs to be adjusted downward, and when the projection of the grating (2) is a circular point, the projection position of the surface of the workpiece (13) is the focal point of the objective lens (11).

[0013] A second aspect of the present application is a mounting and confocal adjustment method of the coaxial focusing system, comprising the following steps:

[0014] The reflecting surfaces of the first half mirror (4), the full mirror (6) and the second half mirror (7) are precisely 45 degrees to the axial direction by using precise mechanical machining parts installation, the center of the grating (2) coincides with the optical axis, the axis of the conjugate light path (14) coincides with the optical axis, the center line of the objective lens (11) coincides with the optical axis, and the center line of the objective lens (11) is perpendicular to the optical axis;

[0015] The focusing tool with a cross at each end is rotated to the mounting position of the objective lens (11), and the projections of the laser beam (60), the first parallel light beam (50) and the first light beam (70) to the two crosses of the focusing tool are adjusted to completely coincide, that is, the laser beam (60), the first parallel light beam (50) and the first light beam (70) have been adjusted to be coaxial with the optical axis.

[0016] The ceramic motor (10) is placed at zero point, specifically, the focusing system is roughly adjusted to be slightly higher than the focal point of the objective lens (11) of the workpiece (13) to be processed, the Z-axis position at this time is recorded, the focusing system is moved downward by equal steps, and the thinnest line in the center line of the marking line is found out according to the set marking line, and the Z-axis position corresponding to the line is the focal point of the focusing system.

[0017] The workpiece (13) to be processed is replaced and a cross is marked on the surface by laser, the light source (1) is turned off, at this time the CCD (3) cannot see a clear cross image, the position of the lens (5) is adjusted up and down until the cross image is clear, that is, the confocal adjustment of the CCD (3) and the laser beam (60) is completed; the light source (1) is turned on, and the position of the grating (2) is adjusted left and right until a cross projection image with sharp edges can be seen on the CCD (3), that is, the confocal adjustment of the projection image and the laser beam (60) is completed.

[0018] The crosshair of the CCD (3) is adjusted horizontally until the crosshair of the CCD (3) and the cross marked by laser completely coincide, that is, the horizontal position calibration of the CCD (3) and the laser beam (60) is completed, at this time the projection imaging light path, the shooting imaging light path and the laser focusing light path are accurately coaxial.

[0019] The further technical scheme of the present application is: calibrating the laser displacement sensor (12), specifically comprising: recording the coordinate position of the cross of the surface of the workpiece (13); moving the light spot of the laser displacement sensor (12) to the center of the cross, at this time the reading of the laser displacement sensor (12) is FFFF or not zero, adjusting the manual knob until the reading of the laser displacement sensor (12) is zero, if the light spot of the laser displacement sensor (12) deviates from the cross center, the light spot is moved to the cross center again through the translation of the XY axis, and the XY coordinate at this time is recorded, and the calibration of the laser displacement sensor is completed.

[0020] The third aspect of the present application is a method for automatic focusing by using the coaxial focusing system for laser precision machining, comprising the following steps:

[0021] The workpiece (13) is moved to the machining position by the linear motor of the XY axis in the laser precision machining equipment, and the coordinates (X1, Y1) are recorded;

[0022] The Z axis position is moved downward from the original position, the Z axis position is preset according to the height of the workpiece (13) (X1, Y1, Z1), and the Z axis position is stopped after moving to the preset position, at this time the workpiece (13) is located below the laser displacement sensor (12);

[0023] The position of the workpiece (13) is measured by the laser displacement sensor (12);

[0024] It is determined whether the reading of the laser displacement sensor (12) is zero, and the reading of the laser displacement sensor (12) is set to zero after the laser displacement sensor (12) and the laser focus are adjusted to be in focus during calibration;

[0025] The workpiece (13) is driven by the XY linear motor, and is switched to below the objective lens (11) according to the calibrated distance, and the coordinates (X2, Y2, Z1) are recorded;

[0026] If the measurement value of the laser displacement sensor (12) is greater than zero, it is located above the focus, the Z axis position is corrected downward with a step distance of 0.5 um, the image is determined once every step, and the cycle is repeated until a clear and sharp image is obtained, that is, the focusing is completed, if the measurement value of the laser displacement sensor (12) is less than zero, the Z axis position is upward;

[0027] The workpiece (13) is moved below the laser displacement sensor (12) by the XY linear motor, the reading of the laser displacement sensor (12) is recorded, and the reading is automatically cleared after completion, and the laser precision machining is completed.

[0028] The further technical scheme of the present application is that the method further comprises automatically tracking the focus point in the laser precision machining process, and comprises the following steps:

[0029] The laser displacement sensor (12) scans the laser machining path and collects the corresponding point Z coordinate at a frequency of 50KHz;

[0030] A focus following file is generated according to the measurement result of the laser displacement sensor (12), and the focus following file is stored in the form of coordinates;

[0031] Switching to the objective lens (11), the objective lens (11) completes laser machining according to the focus following file.

[0032] The present application provides a coaxial focusing system applied to laser precision machining, a mounting method and a focusing method, which is based on coaxial conjugate light path, combined with accurate measurement of laser displacement sensor, overcomes the shortcomings of pure optical measurement and image comparison focusing method, realizes high-speed and high-precision focusing and high-speed focus following function, and provides the best solution for laser machining of products with thickness deviation and surface deformation. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is a coaxial focusing system structure schematic diagram for laser precision machining in the embodiment of the present application;

[0034] Figure 2 is a projection imaging light path schematic diagram in the embodiment of the present application;

[0035] Figure 3 is a projection imaging light path schematic diagram in the embodiment of the present application;

[0036] Figure 4 is a laser focusing light path schematic diagram in the embodiment of the present application;

[0037] Figure 5 is a focusing schematic diagram realized by shape comparison method in the embodiment of the present application;

[0038] Figure 6 is a focusing tool structure schematic diagram used in the focusing adjustment process of the embodiment of the present application;

[0039] Figure 7 is a cross projection situation schematic diagram of the focusing tool in the focusing adjustment process of the embodiment of the present application;

[0040] Figure 8 is a line marking schematic diagram used in the focusing adjustment process of the embodiment of the present application;

[0041] Figure 9 is an automatic focusing work flow schematic diagram of the coaxial focusing system in the embodiment of the present application;

[0042] Figure 10 is a schematic diagram of the automatic focus tracking workflow of the coaxial focusing system in the embodiment of the present application;

[0043] The figure legend is as follows: 1, light source, 2, grating, 3, CCD, 4, first half mirror, 5, lens, 6, full mirror, 7, second half mirror, 8, laser system, 9, beam expander, 10, ceramic motor, 11, objective lens, 12, laser displacement sensor, 13, workpiece, 14, conjugate light path, 50, first parallel light beam, 51, first divergent light beam, 52, second divergent light beam, 53, second parallel light beam, 54, third parallel light beam, 55, fourth parallel light beam, 70, first light beam, 71, fifth parallel light beam, 72, sixth parallel light beam, 73, seventh parallel light beam, 74, second light beam, 75, third light beam, 76, eighth parallel light beam, 77, fourth light beam, 60, laser beam, 61, ninth parallel light beam, 62, tenth parallel light beam. DETAILED DESCRIPTION

[0044] The present application will be further described below in conjunction with the drawings and examples. It can be understood that the specific examples described herein are only used to explain the present application, and are not a limitation on the present application. In addition, it should be noted that, for the convenience of description, only the relevant part of the present application is shown in the drawings, and not all structures.

[0045] Before discussing the example embodiments in more detail, it should be mentioned that some of the example embodiments are described as processes or methods depicted as flow charts. Although the steps of the processes are depicted in a sequential order, many of the steps can be performed in parallel, concurrently or simultaneously with one another. In addition, the order of the steps can be re-arranged. The processes can be terminated when their operations are completed, but can also have additional steps not included in the figure, which can also be performed after the operations of the processes are completed. The processes can correspond to methods, functions, procedures, subroutines, subprograms, etc.

[0046] Moreover, the terms "first", "second", "third", and the like can be used herein to describe various directions, actions, steps, or elements, etc. but such directions, actions, steps, or elements should not be limited by such terms. The terms are only used to distinguish one direction, action, step, or element from another direction, action, step, or element. For example, a first parallel light beam can be called a second parallel light beam, and similarly, a second parallel light beam can be called a first parallel light beam, without departing from the scope of the present application. Both the first parallel light beam and the second parallel light beam are parallel light beams, but they are not the same parallel light beam. The terms "first", "second", and the like should not be understood as indicating or implying relative importance or an indicated number of technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "a plurality of" is at least two, for example, two, three, etc., unless otherwise explicitly specified.

[0047] The embodiments of the present application are directed to a coaxial focusing system for laser precision machining and a mounting method and a focusing method, and provide the following embodiments:

[0048] Referring to Figure 1 , Figure 2 , FIG. 1 is a structural schematic diagram of a coaxial focusing system for laser precision machining in an embodiment, which comprises, in sequence along a projection imaging light path, a light source 1, a grating 2, a first half mirror 4, a lens 5, a full mirror 6, a second half mirror 7, an objective lens 11, and a workpiece 13 to be machined. The grating 2 diffracts a first parallel light beam 50 emitted by the light source 1 into a first divergent light beam 51. The first half mirror 4 reflects the first divergent light beam 51 into a second divergent light beam 52. The lens 5 converges the second divergent light beam 52 into a second parallel light beam 53. The full mirror 6 reflects the second parallel light beam 53 into a third parallel light beam 54. The second half mirror 7 reflects the third parallel light beam 54 into a fourth parallel light beam 55. The objective lens 11 converges and projects the fourth parallel light beam 55 onto the workpiece 13 to be machined. The lens 5 and the objective lens 11 form a pair of conjugate lenses, and the focal points are located at the grating 2 and the surface of the workpiece 13 to be machined, respectively. The grating 2 realizes projection imaging on the workpiece 13 to be machined based on the principle of conjugate imaging. Specifically, according to the principle of conjugate light path imaging, a clear real image that is exactly the same in shape as the grating 2 and is enlarged or reduced will be projected on the surface of the workpiece 13 to be machined. According to the principle of conjugate imaging, the size of the projected real image is S 像 = (F 透镜 / F 物镜 )*S 光栅 .

[0049] Referring to Figure 3The to-be-processed piece 13, the objective lens 11, the second half mirror 7, the total reflection mirror 6, the lens 5, the first half mirror 4, the conjugate light path 14 and the CCD 3 are sequentially arranged along a photographing light path, wherein the to-be-processed piece 13 reflects a projection image as a first light beam 70, the objective lens 11 converges the first light beam 70 into a fifth parallel light beam 71, the second half mirror 7 reflects the fifth parallel light beam 71 into a sixth parallel light beam 72, the total reflection mirror 6 reflects the sixth parallel light beam 72 into a seventh parallel light beam 73, the lens 5 converges the seventh parallel light beam 73 into a second light beam 74, the first half mirror 4 converges the second light beam 74 into a third light beam 75, the conjugate light path 14 converges the third light beam 75 into an eighth parallel light beam 76 and then converges the eighth parallel light beam 76 into a fourth light beam 77, and the fourth light beam 77 is projected to the CCD 3 to obtain a same enlarged image as the grating 2, one of the focal points of the conjugate light path 14 is symmetrical to the grating 2 with the first half mirror 4 as a symmetrical axis, and the other focal point of the conjugate light path 14 is located on a photosensitive element of the CCD 3, preferably, when the magnification of the conjugate light path 14 is λ1 and the magnification of a set of conjugate light paths formed by the lens 5 and the objective lens 11 is λ2, the magnification of the image obtained at the CCD is λ = λ1 * λ2.

[0050] Referring to Figure 4 The laser system 8, the beam expander 9, the total reflection mirror 6, the second half mirror 7, the objective lens 11 and the to-be-processed piece 13 are sequentially arranged along a laser focusing light path, wherein the laser system 8 is used for emitting a laser beam 60, the beam expander 9 expands the laser beam 60 into a ninth parallel light beam 61, the ninth parallel light beam 61 is deflected by the total reflection mirror 6 and offset by the second half mirror 7 into a tenth parallel light beam 62, and the objective lens 11 focuses the tenth parallel light beam 62 to the to-be-processed piece 13.

[0051] Referring to Figures 1-4 The objective lens 11 is provided with the ceramic motor 10, and the ceramic motor 10 is located at zero point; it should be noted that the ceramic motor 10 is a hollow structure, and the light beam can pass through without hindrance.

[0052] The coaxial focusing system further comprises a laser displacement sensor 12 for measuring the relative distance between the to-be-processed piece 13 and the objective lens 11.

[0053] The light source 1 in the coaxial focusing system embodiment of the application is an LED point light source or an LD laser light source. Specifically, the LED point light source is white light W, red light R, green light G, blue light B, infrared light IR or ultraviolet UV, has a power of 0.4-5W, an aperture of 8-30mm and a general / high-brightness optional light emission form; or the LD laser light source has a wavelength of 605-808nm, a power of ≦500mW and an aperture of 8-12mm.

[0054] The grating 2 in the coaxial focusing system embodiment of the present application is light shielding or light transmitting, and the slit width is 50-500um.

[0055] The CCD 3 in the coaxial focusing system embodiment of the present application is a 2000W pixel industrial camera.

[0056] The first half mirror 4 in the coaxial focusing system embodiment of the present application is a 25.5*36*2.5mm 45-degree half-transmission film, and the transmittance of white light, RGB light, IR light and UV light is 50%.

[0057] The lens 5 in the coaxial focusing system embodiment of the present application is a 25.4mm diameter BK9 flat convex thin lens coated with RGB anti-reflection film, and the focal length is 50-150mm.

[0058] The total reflection mirror 6 in the coaxial focusing system embodiment of the present application is a 25.5*36*2.5mm 45-degree total reflection film, and can reflect white light, RGB light, IR light, UV light and laser with a reflectivity of 100%.

[0059] The second half mirror 7 in the coaxial focusing system embodiment of the present application is a 25.5*36*2.5mm 45-degree half-transmission film, and the transmittance of laser is 100%, and the reflectivity of white light, RGB light and IR light is 100%.

[0060] The laser system 8 in the coaxial focusing system embodiment of the present application has a wavelength range of 10-3000nm and a power range of 10mW-200W.

[0061] The beam expander 9 in the coaxial focusing system embodiment of the present application has a wavelength range of 10-3000nm, and the collimation multiple is 1-10X.

[0062] The ceramic motor 10, also known as objective lens positioner, in the coaxial focusing system embodiment of the present application has a load capacity of ≦400g, a response frequency of ≦100KHz, and an interface size of M26x0.706.

[0063] The objective lens 11 in the coaxial focusing system embodiment of the present application is a laser transmitting objective lens, and has a magnification of 2X, 5X, 10X, 20X, 50X and 100X, a numerical aperture of 0.14-0.7, a working distance of 10-37.5mm, a focal length of 2-40mm, and a resolution of 0.4-2um.

[0064] The laser displacement sensor 12 in the coaxial focusing system embodiment of the present application has a detection distance of 5-190mm, a detection accuracy of ±0.02%, a reproducibility of 0.01-0.5um, a sampling frequency of 50KHz, and an application range including but not limited to metal, semiconductor, LCD, plastic, rubber and other materials, and material characteristics including but not limited to transparent, translucent, mirror reflection and diffuse reflection.

[0065] The magnification of the conjugate light path 14 in the coaxial focusing system embodiment of the present application is 5X, 10X, 20X, or 50X.

[0066] The lens 5 and the objective lens 11 form a set of conjugate light paths in the coaxial focusing system embodiment of the present application; the conjugate light path 14 is another set of conjugate light paths.

[0067] The light beams 50-55, the light beams 60-64, and the light beams 70-75 are coaxial light paths in the coaxial focusing system embodiment of the present application. Figure 1 The arrows drawn represent the direction of light path propagation.

[0068] In a preferred embodiment, the coating materials of the lenses, the half mirror, and the full mirror are different according to the selected point light source and the wavelength band of the laser system; the lenses are achromatic lenses, and preferably, the coating is a 45-degree coating and a 90-degree coating.

[0069] In a specific embodiment, the system is used in a laser processing system, and the XYZ three-axis, the laser focal point, and the measurement point of the laser displacement sensor need to be accurately calibrated in the XY coordinate and Z-axis coordinate directions. In the calibration process, the planar calibration plate and the ceramic motor are positioned at the zero point.

[0070] In a preferred embodiment, when the light source 1 is an LED point light source, the focusing is achieved by using the sharpness contrast method, specifically: according to the principle of conjugate imaging, when the grating 2 projects the clearest image on the surface of the workpiece 13, the surface of the workpiece 13 is just located at the focal point of the objective lens 11; the entire focusing system is adjusted up and down, so that the CCD 3 obtains the sharpest clear image, and at this time, the projection position of the surface of the workpiece 13 is the focal point of the objective lens 11.

[0071] Referring to Figure 5 In another preferred embodiment, when the light source 1 is an LD laser light source, the focusing is achieved by using the shape contrast method, specifically: the grating 2 is a semicircular structure, according to the principle of conjugate imaging, when the projection of the grating 2 is a right semicircle, the focal point is located above the surface of the workpiece 13, at this time, the optical system needs to be adjusted downward; when the projection of the grating 2 is a left semicircle, the focal point is located below the surface of the workpiece 13, at this time, the optical system needs to be adjusted upward; when the projection of the grating 2 is exactly a circular point, the projection position of the surface of the workpiece 13 is the focal point of the objective lens 11.

[0072] Another embodiment of the present application is a mounting and confocal adjustment method of the above-mentioned coaxial focusing system, which comprises the following steps:

[0073] The first half mirror 4, the total reflection mirror 6 and the second half mirror 7 are installed by precise mechanical processing parts, and the reflecting surfaces of the mirrors are in precise 45 degrees with the axial direction, the center of the grating 2 coincides with the optical axis, the axis of the conjugate light path 14 coincides with the optical axis, the center line of the objective lens 11 coincides with the optical axis, and the center line of the objective lens 11 is perpendicular to the optical axis;

[0074] Referring to Figure 6 、 Figure 7 , the focusing tool with a cross at each end is rotated to the installation position of the objective lens 11, and the laser beam 60, the first parallel light beam 50 and the first light beam 70 are adjusted to the two crosses of the focusing tool respectively, and the projections of the two crosses are completely overlapped, which means that the laser beam 60, the first parallel light beam 50 and the first light beam 70 have been adjusted to be coaxial with the optical axis; specifically, by means of the focusing tool shown in Figure 6 , with threaded installation, various adapter sleeves can be connected, and there is a cross at each end, which is rotated to the installation position of the objective lens 11, and the projections of the two crosses are not overlapped under the condition that the light path is not adjusted, as shown in Figure 7 , the angle of incidence of the laser beam 60 is adjusted, and the projections of the two crosses of the focusing tool are completely overlapped, as shown in Figure 7 , at this time, it means that the laser beam has been adjusted to be coaxial with the optical axis. The light path devices of the light source 1 and the light path devices of the CCD 3 are adjusted by the same tool and method, and at this time, the three main light paths basically reach coaxial.

[0075] In the specific implementation process, the ceramic motor 10 is placed at zero, the focusing system is roughly adjusted to be slightly higher than the focal point of the objective lens 11 from the workpiece 13 to be processed, the Z-axis position at this time is recorded, the focusing system is moved downward by 0.05mm, and the scale line shown in Figure 8 is marked, the width of the scale line will become thin and then thick again, and the thinnest line is found by using two-dimensional, and the Z-axis position corresponding to the line is the focal point of the focusing system.

[0076] The workpiece 13 to be processed is replaced and a cross is engraved on the surface by laser, the light source 1 is turned off, the position of the lens 5 is adjusted up and down until the cross image is clear, which completes the confocal adjustment of the CCD 3 and the laser beam 60; the light source 1 is turned on, and the position of the grating 2 is adjusted left and right until a clear cross projection image with sharp edges can be seen on the CCD 3, which completes the confocal adjustment of the projection image and the laser beam 60;

[0077] Further, the cross cursor of the CCD 3 is adjusted horizontally until the cross cursor of the CCD 3 and the cross engraved by laser are completely overlapped, which completes the horizontal position calibration of the CCD 3 and the laser beam 60, and at this time, the projection imaging light path, the shooting imaging light path and the laser focusing light path reach accurate coaxial.

[0078] Further, the calibration of the laser displacement sensor 12 specifically includes: recording the coordinate position of the cross of the surface of the workpiece 13 to be processed; moving the light spot of the laser displacement sensor 12 to the center of the cross, at this time, the reading of the laser displacement sensor 12 is FFFF or not zero, adjusting the manual knob until the reading of the laser displacement sensor 12 is zero, if the light spot of the laser displacement sensor 12 deviates from the cross center, the light spot is moved to the cross center again through the translation of the XY axis, the XY coordinate at this time is recorded, and the calibration of the laser displacement sensor is completed.

[0079] Another embodiment of the present application is a method for automatic focusing by using the coaxial focusing system for laser precision machining, in the embodiment, the coaxial focusing system is matched with a laser machining system with XYZ three axes, a height measuring module and an electrical control, see Figure 9 , and the implementation process is as follows:

[0080] The laser machining system is started from the reset state, the XYZ is located at the loading origin point, the coordinate is (0, 0, 0), the ceramic motor is located at the zero point, the workpiece 13 to be processed is fixed by vacuum adsorption and moved to the processing position by the XY linear motor, the coordinate is (X1, Y1);

[0081] The Z axis position is moved downward from the original position, the Z axis position (X1, Y1, Z1) is preset according to the height of the workpiece 13 to be processed, the Z axis position is stopped after moving to the preset position, at this time, the workpiece 13 to be processed is located below the laser displacement sensor;

[0082] The position of the workpiece 13 to be processed is measured by using the laser displacement sensor 12;

[0083] It is determined whether the reading of the laser displacement sensor 12 is zero. In the calibration, the laser displacement sensor 12 is adjusted to be in focus with the laser focus point, and the reading of the laser displacement sensor 12 is zero, which can determine that the workpiece 13 to be processed is located at the laser focus point. In fact, this situation almost does not occur, and in order to eliminate the interference of the external environment on the laser displacement sensor 12, the laser displacement sensor 12 is generally not used for direct focusing;

[0084] The workpiece 13 to be processed is driven by the XY linear motor, and is switched to below the objective lens 11 according to the calibrated distance, the coordinate is (X2, Y2, Z1);

[0085] According to the measurement value of the laser displacement sensor 12, if greater than zero, it is above the focal point, the Z-axis position is corrected downward with a step distance of 0.5um, and the image is determined once every movement step. The determination standard of the image can be determined by the software algorithm. The cycle is repeated until a clear and sharp image is determined, and the focusing is completed. Otherwise, it is below the focal point, and the step direction of the Z-axis position is opposite. The step distance determines the focusing accuracy. If a more accurate focusing accuracy is required, the step distance can be reduced. The minimum step distance can be set to 0.1um, and the maximum step distance cannot exceed 1um.

[0086] The XY linear motor is used to drive the workpiece 13 to move under the laser displacement sensor 12, and the laser displacement sensor 12 reads the value. After reading, the software automatically clears the zero, and the processing is completed.

[0087] Further, the method for automatic focusing of the coaxial focusing system for laser precision machining in the embodiment further includes automatic tracking of the focal point during laser precision machining, as shown in Figure 10 , comprising the following steps:

[0088] The laser displacement sensor 12 scans the laser processing path and collects the corresponding point Z coordinates at a frequency of 50KHz. It should be noted that the response point can be manually set by the operator or automatically generated according to the sampling frequency and the attack speed.

[0089] According to the measurement result of the laser displacement sensor 12, a focal point tracking file is generated, and the focal point tracking file is stored in the form of coordinates;

[0090] Switch to the objective lens 11, and the objective lens 11 completes the laser processing according to the focal point tracking file.

[0091] The coaxial focusing system for laser precision machining, the installation method and the focusing method provided by the above embodiments overcome the shortcomings of pure optical measurement and image comparison focusing method, realize high-speed and high-precision focusing and high-speed focal point tracking function, and provide the best solution for laser processing of products with thickness deviation and surface deformation.

[0092] Note that the above is only the preferred embodiment of the present application and the technical principle applied. Those skilled in the art will understand that the present application is not limited to the specific embodiments described herein, and those skilled in the art can make various obvious changes, re-adjustments and substitutions without departing from the scope of the present application. Therefore, although the present application has been described in detail through the above embodiments, the present application is not limited to the above embodiments, and can include more other equivalent embodiments without departing from the concept of the present application, and the scope of the present application is determined by the scope of the appended claims.

Claims

1. A coaxial focusing system for laser precision machining, characterized in that, The application relates to a projection imaging device and method. The device comprises a light source (1), a grating (2), a first half mirror (4), a lens (5), a full mirror (6), a second half mirror (7), an objective lens (11) and a workpiece (13) arranged in sequence along a projection imaging light path, wherein the grating (2) diffracts a first parallel light beam (50) emitted by the LED light source (1) into a first divergent light beam (51), the first half mirror (4) reflects the first divergent light beam (51) into a second divergent light beam (52), the lens (5) converges the second divergent light beam (52) into a second parallel light beam (53), the full mirror (6) reflects the second parallel light beam (53) into a third parallel light beam (54), the second half mirror (7) reflects the third parallel light beam (54) into a fourth parallel light beam (55), and the objective lens (11) converges and projects the fourth parallel light beam (55) onto the workpiece (13); the lens (5) and the objective lens (11) form a pair of conjugate lenses, and the focal points are located on the grating (2) and the surface of the workpiece (13) respectively, and the grating (2) realizes projection imaging based on the principle of conjugate imaging on the workpiece (13). The device further comprises the workpiece (13), the objective lens (11), the second half mirror (7), the full mirror (6), the lens (5), the first half mirror (4), a conjugate light path (14) and a CCD (3) arranged in sequence along a shooting light path, wherein the workpiece (13) reflects the projection imaging into a first light beam (70), the objective lens (11) converges the first light beam (70) into a fifth parallel light beam (71), the second half mirror (7) reflects the fifth parallel light beam (71) into a sixth parallel light beam (72), the full mirror (6) reflects the sixth parallel light beam (72) into a seventh parallel light beam (73), the lens (5) converges the seventh parallel light beam (73) into a second light beam (74), the first half mirror (4) converges the second light beam (74) into a third light beam (75), the conjugate light path (14) converges the third light beam (75) into an eighth parallel light beam (76) firstly, and converges the eighth parallel light beam (76) into a fourth light beam (77) secondly, and the fourth light beam (77) is projected onto the CCD (3) to obtain the same enlarged image as the grating (2), one of the focal points of the conjugate light path (14) is symmetrical to the grating (2) with the half mirror (4) as the symmetrical axis, and the other focal point of the conjugate light path (14) is located on the photosensitive element of the CCD (3). A laser system (8), a beam expander (9), a total reflection mirror (6), a second half mirror (7), an objective lens (11), and a workpiece (13) are arranged along a laser focusing light path in sequence, wherein the laser system (8) is used for emitting a laser beam (60), the beam expander (9) expands the laser beam (60) into a ninth parallel light beam (61), the ninth parallel light beam (61) is deflected by the total reflection mirror (6) and offset by the second half mirror (7) into a tenth parallel light beam (62), and the tenth parallel light beam (62) is focused by the objective lens (11) onto the workpiece (13); The objective lens (11) is provided with a ceramic motor (10), and the ceramic motor (10) is arranged at a zero point; The coaxial focusing system further comprises a laser displacement sensor (12) for measuring the relative distance between the workpiece (13) and the objective lens (11).

2. The coaxial focusing system for laser precision machining according to claim 1, characterized in that, The light source (1) is an LED point light source or an LD laser light source.

3. The coaxial focusing system for laser precision machining according to claim 1, characterized in that, When the light source (1) is an LED point light source, focusing is achieved by using a definition contrast method, specifically: according to the principle of conjugate light path imaging, when the grating (2) is projected most clearly on the surface of the workpiece (13), the surface of the workpiece (13) is just located at the focal point position of the objective lens (11), the entire focusing system is adjusted up and down, the CCD (3) obtains a clear image with the sharpest edge, and at this time, the projection position of the surface of the workpiece (13) is the focal point of the objective lens (11).

4. The coaxial focusing system for laser precision machining according to claim 1, characterized in that, When the light source (1) is an LD laser light source, focusing is achieved by using a shape contrast method, specifically: the grating (2) is a semicircular structure, according to the principle of conjugate imaging, when the projection of the grating (2) is a semicircle on one side, the corresponding focal point is located below the surface of the workpiece (13), the focusing system needs to be adjusted upward, when the projection of the grating (2) is a semicircle on the other side, the corresponding focal point is located above the surface of the workpiece (13), the focusing system needs to be adjusted downward, and when the projection of the grating (2) is a circular dot, at this time, the projection position of the surface of the workpiece (13) is the focal point of the objective lens (11).

5. A method of installing and confocal adjusting the coaxial focusing system of any of claims 1-2, characterized by, The steps include: Precise mechanical machining parts are used to install the reflecting surfaces of the first half mirror (4), the total reflection mirror (6), and the second half mirror (7) to be precisely 45 degrees with the axial direction, the center of the grating (2) coincides with the optical axis, the axis of the conjugate light path (14) coincides with the optical axis, the center line of the objective lens (11) coincides with the optical axis, and the center line of the objective lens (11) is perpendicular to the optical axis; A focusing tool with a cross at each end is rotated to the installation position of the objective lens (11), the projections of the laser beam (60), the first parallel light beam (50), and the first light beam (70) to the two crosses of the focusing tool are adjusted to completely coincide, which indicates that the laser beam (60), the first parallel light beam (50), and the first light beam (70) have all been adjusted to be coaxial with the optical axis. The ceramic motor (10) is placed at zero point, specifically: the focusing system is roughly adjusted to the workpiece (13) slightly higher than the objective lens (11) focal point, the Z-axis position at this time is recorded, the focusing system is moved downward by equal steps, and the thinnest line in the cross line is found according to the set scale line, and the Z-axis position corresponding to the line is the focal point position of the focusing system; The workpiece (13) is replaced and a cross is engraved on the surface by laser, the light source (1) is turned off, at this time the CCD (3) cannot see a clear cross image, the position of the lens (5) is adjusted up and down until the cross image is clear, that is, the confocal adjustment of the CCD (3) and the laser beam (60) is completed; the light source (1) is turned on, and the position of the grating (2) is adjusted left and right until a cross projection image with sharp edges can be seen on the CCD (3), that is, the confocal adjustment of the projection image and the laser beam (60) is completed; The cross cursor of the CCD (3) is adjusted horizontally until the cross cursor of the CCD (3) and the cross engraved by laser are completely overlapped, that is, the horizontal position calibration of the CCD (3) and the laser beam (60) is completed, at this time the projection imaging light path, the shooting imaging light path and the laser focusing light path are accurately coaxial.

6. The mounting and confocal adjustment method according to claim 5, wherein, The laser displacement sensor (12) is calibrated, specifically including: recording the coordinate position of the cross on the surface of the workpiece (13); moving the laser displacement sensor (12) light point to the cross center, at this time the laser displacement sensor (12) reading is FFFF or not zero, adjusting the manual knob until the laser displacement sensor (12) reading is zero, if the laser displacement sensor (12) light point deviates from the cross center, the light point is moved to the cross center again by translating the XY axis, and the XY coordinate at this time is recorded, and the laser displacement sensor calibration is completed.

7. A method for auto-focusing with the coaxial focusing system for laser precision machining according to any one of claims 1-2, characterized in that, The steps include: The workpiece (13) moves to the workpiece position along with the XY linear motor in the laser precision machining equipment, and the coordinates (X1, Y1) are obtained; The Z-axis position moves downward from the original position, and the Z-axis position is preset according to the height of the workpiece (13) (X1, Y1, Z1), and the Z-axis position stops after moving to the preset position, at this time the workpiece (13) is located below the laser displacement sensor (12); The position of the workpiece (13) is measured by the laser displacement sensor (12); It is determined whether the reading of the laser displacement sensor (12) is zero, and the reading of the laser displacement sensor (12) is set to zero after the laser displacement sensor (12) is adjusted to be confocal with the laser focal point during calibration; The workpiece (13) is driven by the XY linear motor, and is switched to below the objective lens (11) according to the calibrated distance, and the coordinates (X2, Y2, Z1) are obtained. If the laser displacement sensor (12) measurement is greater than zero, it is above the focal point, the Z-axis position is corrected downward with a step distance of 0.5um, and the image is determined once for every movement step to see if it is clear, and the cycle is repeated until a clear sharp image is obtained, i.e. the focusing is completed, if the laser displacement sensor (12) measurement is less than zero, it is below the focal point, and the Z-axis position step direction is upward; The XY linear motor drives the workpiece (13) to move under the laser displacement sensor (12), the laser displacement sensor (12) reads, and automatically clears zero after reading, and the laser precision machining is ready.

8. The autofocusing method of claim 7, wherein, The method further comprises automatically tracking the focal point during laser precision machining, comprising the following steps: The laser displacement sensor (12) scans the laser processing path and collects the corresponding point Z coordinate at a frequency of 50KHz; According to the measurement results of the laser displacement sensor (12), a focal point following file is generated, and the focal point following file is stored in the form of coordinates; Switch to the objective lens (11), and the objective lens (11) completes the laser processing according to the focal point following file.

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