Monocrystalline silicon aspherical lens and numerical control polishing process thereof

Abstract

The invention relates to the technical field of optical processing, and provides a monocrystalline silicon aspherical lens and a numerical control polishing process thereof, a numerical control polishing machine is used for carrying out the main steps of rough polishing, fine polishing, fine trimming and the like, process parameters are adjusted according to the characteristics of monocrystalline silicon, and therefore the monocrystalline silicon aspherical lens with the diameter smaller than 320 mm can be polished. By means of a numerical control polishing machine tool, the optimized front surface type PV can reach 0.3 mu m or below, the surface smoothness can reach 40 / 20, and the method has reference significance for monocrystalline silicon aspherical lenses with the diameter of 320 mm or above.

Description

Technical Field

[0001] The present application relates to the field of optical processing technology, and specifically to a single-crystal silicon aspheric lens and a numerical control polishing process thereof. Background Art

[0002] Aspherical lenses are available in shapes such as parabolas, quadratic curves, cubic curves or higher-order curves. During the design process, these lenses take full account of correction factors such as aberrations, chromatic aberrations and spherical aberrations. Usually, one aspherical lens can achieve the correction effect of multiple spherical lenses, thus reducing the number of lenses required. This not only improves the precision and clarity of the lens, but also enhances the accuracy of color reproduction, while reducing the reflection of light inside the lens and reducing the size of the lens. Aspherical lenses also have the characteristics of high zoom, short object distance and large aperture. High zoom simplifies the types of lenses, short object distance is suitable for close-up shooting, and large aperture can perform well in low-light environments. These advantages make the application fields of aspherical lenses increasingly wide.

[0003] Single crystal silicon is widely used in infrared optics due to its advantages of low density, high hardness, high transmittance, low self-luminescence and low cost. Although the high hardness of single crystal silicon brings good performance, its processing difficulty means that grinding and polishing technology is still used to produce spherical lenses in most cases in the infrared field.

[0004] In recent years, with the increasing recognition of the superior performance of aspheric lenses, many infrared optical designers have begun to try to design silicon lenses as aspheric lenses. However, the production of single-crystal silicon aspheric lenses remains a major challenge for companies. At present, single-crystal silicon aspheric lenses with a diameter of less than 30 mm can be processed using ultra-precision single-point lathes. For example, CN112496876A discloses an ultra-precision turning method for the aspheric surface of a silicon lens. However, since the Mohs hardness of silicon materials reaches 7, diamond tools are prone to wear, resulting in the need for frequent tool replacement, which increases production costs. In addition, the surface produced by the single-point turning process usually has "rainbow patterns" and "Mercedes-Benz patterns" unique to single-crystal silicon, and the surface finish is poor.

[0005] CN110682185A discloses a high-precision exposure lens processing method for pulse compression grating production, including the construction of a self-collimating interference detection device, milling, grinding, precision polishing and smoothing of the aspheric surface of the exposure lens. The full-band wavefront quality under the exposure wavelength is improved. However, it is not suitable for the production of aspheric lenses of all materials, especially for the production of single-crystal silicon aspheric lenses, because single-crystal silicon aspheric lenses also have different hardness in different directions, which is reflected in the characteristics of high hardness in the center and low hardness at the edge. Summary of the invention

[0006] In order to solve the above technical problems, the present application provides a CNC polishing process for single-crystal silicon aspheric lenses. This polishing process can polish single-crystal silicon aspheric lenses with a diameter of less than 320 mm. With the help of CNC polishing machines, the optimized front PV can be made to be less than 0.3 μm, and the surface finish can reach 40 / 20. It is also of reference significance for single-crystal silicon aspheric lenses with a diameter of more than 320 mm.

[0007] The technical solution of this application is:

[0008] A single crystal silicon aspheric lens numerical control polishing process comprises the following steps:

[0009] Step 1: Scan the profile of the single crystal silicon aspheric lens to obtain a profile model;

[0010] Step 2: Fix the single crystal silicon aspheric lens and its tooling in the CNC polishing machine, import the contour model into the CNC polishing machine to calculate the rough polishing program and start rough polishing;

[0011] Step 3: Perform profile scanning on the single crystal silicon aspheric lens after rough polishing to obtain a new profile model;

[0012] If the PV of the surface is greater than the drawing requirements, return to step 2; if the PV of the surface is less than the drawing requirements, go to step 4;

[0013] Step 4: Fix the single crystal silicon aspheric lens and its tooling in the CNC polishing machine again, and import the contour model obtained in step 3 into the CNC polishing machine to calculate the fine polishing program and start fine polishing to obtain a semi-finished product;

[0014] Step 5: Refine the semi-finished product to obtain the finished product;

[0015] Among them, the settings of the CNC polishing machine meet the following conditions:

[0016] Setting a: When the lens diameter is set to be less than 150 mm and the particle size of the polishing liquid is 0.5 to 1 μm, the speed of the polishing head and the workpiece axis of the CNC polishing machine are set to 800 to 1000 RPM, and the downward pressure is 0.5 to 0.7 mm;

[0017] Setting b: When the lens diameter is set to be greater than 150 mm and the particle size of the polishing liquid is 0.5 to 1 μm, the speed of the polishing head and the workpiece axis of the CNC polishing machine is set to 300 to 500 RPM, and the downward pressure is 0.5 to 0.7 mm;

[0018] Setting c: When the lens diameter is set to be less than 150 mm and the particle size of the polishing liquid is 2 to 3 μm, the speed of the polishing head and the workpiece axis of the CNC polishing machine is set to 300 to 500 RPM, and the downward pressure is 0.2 to 0.4 mm;

[0019] Setting d: When the lens diameter is set to be greater than 150 mm and the particle size of the polishing liquid is 2 to 3 μm, the speed of the polishing head and the workpiece axis of the CNC polishing machine are set to 150 to 300 RPM, and the downward pressure is 0.2 to 0.4 mm.

[0020] In actual application, the present application adjusts the setting parameters of the CNC polishing machine according to the lens and the polishing liquid, so as to avoid the CNC polishing machine damaging the single crystal silicon aspheric lens and causing irreparable defects, and can reduce the intermediate frequency error.

[0021] In the above-mentioned single crystal silicon aspheric lens CNC polishing process, in step 3, if the PV of the surface shape is greater than the requirements of the drawing, first determine whether the single crystal silicon aspheric lens is astigmatic according to the contour model;

[0022] If yes, perform astigmatism correction and return to step 3; if no, return to step 2.

[0023] In the above-mentioned CNC polishing process for single crystal silicon aspheric lenses, the polishing liquid in step 2 is a mixture of diamond powder, aluminum oxide, silicon dioxide, oily suspension, and pure water, and is mixed in a ratio of 2:1:2:6:29; the polishing head in step 2 uses a polishing leather made of polyurethane material.

[0024] In the above-mentioned single crystal silicon aspheric lens CNC polishing process, the remaining settings of the CNC polishing machine in step 2 are as follows:

[0025] The lens diameter is set to the actual lens diameter + 5 to 10 mm. The reason is that due to the edge collapse phenomenon in the CNC polishing process, the edge surface shape has a sudden change that cannot be controlled. Therefore, when following the polishing trajectory, the polishing head moves a little further outside the lens to reduce the edge collapse phenomenon.

[0026] Correction is set to -130% to -180%;

[0027] The track-pitch value in the path data is one percent of the set lens diameter;

[0028] The unit of oscillation-time is seconds, and its value is 3 to 5 times the set lens diameter;

[0029] The filter width in extrapolate is 1% of the set lens diameter, the point distance is 1% of the set lens diameter, and the target diameter is the effective diameter plus 5 to 10 mm;

[0030] Smoothing is performed, and the smoothing value is 2 to 3 μm;

[0031] Set the min.height to 0-0.2 μm, adjust the removal-coefficient and oscillation-time values, and adjust the feed min. value to 10 mm / min.

[0032] In the above-mentioned single crystal silicon aspheric lens CNC polishing process, the settings of the CNC polishing machine in step 4 are as follows:

[0033] The particle size of the polishing liquid is 0.5-1μm, the downward pressure is 0.1-0.2mm, and the other setting requirements are the same as rough polishing.

[0034] In the above-mentioned CNC polishing process of single crystal silicon aspheric lens, the step 5 transfers the semi-finished product to the grinding and polishing machine, and rotates the semi-finished product at a speed of 100 to 200 RPM, and then uses polishing leather to fine-tune the semi-finished product at a pressure of 2 to 4 kPa.

[0035] In the above-mentioned CNC polishing process for single crystal silicon aspheric lens, before step 1, milling is used to prepare a single crystal silicon aspheric lens with a surface type PV ≤ 2 μm, and the sharp edges at the edge of the single crystal silicon aspheric lens are removed.

[0036] In the above-mentioned CNC polishing process for the single crystal silicon aspheric lens, the size of the polishing head is one third to one quarter of the set lens diameter.

[0037] In the above-mentioned CNC polishing process for single crystal silicon aspheric lenses, in step 2, the actual indentation diameter is compared with the theoretical calculated indentation size, and the rough polishing tooling height is adjusted according to the difference to make the theoretical indentation equal to the actual indentation size.

[0038] The present application also discloses a single crystal silicon aspheric lens, the diameter of which is less than 320 mm, and which is made by the above-mentioned single crystal silicon aspheric lens numerical control polishing process, and the global surface PV reaches less than 0.3 microns, and the surface finish reaches 40 / 20.

[0039] One of the above technical solutions of the present application has at least one of the following advantages or beneficial effects:

[0040] The polishing process of the present application is capable of polishing single-crystal silicon aspheric lenses with a diameter of less than 320 mm. With the help of a CNC polishing machine, the optimized front-type PV can be reduced to less than 0.3 μm, and the surface finish can reach 40 / 20.

[0041] At the same time, compared with single-point turning, the use of polishing to process single-crystal silicon aspheric lenses can overcome the problems of "rainbow patterns" and "Mercedes-Benz patterns" on the surface caused by single-point turning, and has higher processing efficiency and lower costs.

[0042] In addition, the present application can also more accurately control the stability of the polishing surface by controlling the amount of downward pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 The optical surface diagram of the aspheric lens obtained in Example 1 of the present invention;

[0044] Figure 2 The optical surface diagram of the aspheric lens obtained in Example 2 of the present invention;

[0045] Figure 3 The optical surface diagram of the aspheric lens obtained in Example 5 of the present invention;

[0046] Figure 4 The optical surface diagram of the aspheric lens obtained in Example 6 of the present invention;

[0047] Figure 5 This is an optical surface diagram of the aspheric lens obtained in Comparative Example 1 of the present invention;

[0048] Figure 6 This is an optical surface diagram of the aspheric lens obtained in Comparative Example 2 of the present invention;

[0049] Figure 7 This is an optical surface diagram of the aspheric lens obtained in Comparative Example 3 of the present invention;

[0050] Figure 8 This is an optical surface diagram of the aspheric lens obtained in Comparative Example 5 of the present invention;

[0051] Fig. 9 This is an optical surface diagram of the aspheric lens obtained in Comparative Example 6 of the present invention;

[0052] Fig.10 This is an optical surface diagram of an aspheric lens obtained in Comparative Example 7 of the present invention;

[0053] Fig.11 It is a schematic diagram of the cooperation between the polishing head and the lens in the fine finishing of the present invention;

[0054] Fig.12 Schematic diagram of the calculated theoretical indentation of the present invention.

[0055] Fig.13 It is a processing flow diagram of the present invention.

[0056] Description of reference numerals:

[0057] 1. Polishing head; 2. Lens. DETAILED DESCRIPTION

[0058] The technical solutions in the embodiments of the present application are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present application.

[0059] In the following examples, the model of the CNC polishing machine is Satis Loh SPS-200; the model of the CNC milling machine is Satis Loh SPM-200; the model of the profilometer is LUPHOSCAN 260HD 3D. In addition, the drawing requires PV < 5.

[0060] Explanation of the parameter settings of the CNC polishing machine in the article:

[0061] correction: edge retention rate; track-pitch value in path data: spiral pitch; oscillation-time: the time required for one round of polishing; filter width in extrapolate: sampling spiral pitch; point distance: sampling point distance; target diameter: target diameter; smooth: smoothing processing; min.Height: removal amount; removal-coefficient: residence time; feed min.: minimum moving speed of the polishing head.

[0062] Example 1

[0063] refer to Figure 1 , a CNC polishing process for a single crystal silicon aspheric lens. In this embodiment, the actual diameter of the single crystal silicon aspheric lens is 42 mm, and its composition includes a mixed solution of diamond powder, aluminum oxide, silicon dioxide, an oily suspension and pure water, and is prepared in a ratio of 2:1:2:6:29; Fig.13 As shown, the following steps are included:

[0064] Milling: Use CNC milling machine to adjust the surface shape of single crystal silicon aspheric lens to less than 2μm, otherwise it will produce medium and high frequency surface shape errors during polishing, and it is difficult to control the surface shape after polishing to less than 0.5μm. It is also necessary to chamfer or sandpaper grind the edge to remove the sharp edges to prevent cutting the polished skin;

[0065] Contour scanning: perform contour scanning on the single-crystal silicon aspheric lens with a surface area of ​​≤2μm to obtain the first contour model;

[0066] Rough polishing: Fix the single crystal silicon aspheric lens and its tooling in the CNC polishing machine, import the first contour model into the CNC polishing machine to calculate the rough polishing program and start rough polishing;

[0067] Contour scanning: Perform contour scanning on the rough-polished single-crystal silicon aspheric lens to obtain a second contour model; and determine the subsequent processing flow based on the surface shape of the second contour model. The determination process is as follows:

[0068] When the PV of the surface is less than the requirements of the drawing, it will enter fine polishing;

[0069] When the PV of the surface is greater than the requirements of the drawing, first observe whether the contour model has astigmatism. The reason is that the hardness of single crystal silicon is different and anisotropic, and the removal efficiency in different places is different, which is easy to cause astigmatism and deformation;

[0070] If there is astigmatism, perform astigmatism correction, and perform contour scanning again after astigmatism correction;

[0071] If there is no astigmatism, the rough polishing procedure is calculated again using the second contour model and rough polishing is performed;

[0072] Repeat the above judgment process until the surface shape of the single crystal silicon aspheric lens is smaller than the drawing requirements and enter the fine polishing stage.

[0073] In this embodiment, the following points need to be explained for rough polishing:

[0074] 1. The settings of the CNC polishing machine for rough polishing are as follows:

[0075] The particle size of the selected polishing liquid is 3 μm and since the lens diameter is set to be less than 150 mm, it meets setting c;

[0076] Therefore, the speed of the polishing head and the workpiece axis of the CNC polishing machine were set to 400RPM and the rotation direction of the polishing head and the workpiece axis was the same, and the downward pressure was 0.2mm;

[0077] The lens diameter is set to the actual lens diameter plus 10mm, that is, the lens diameter is set to 52mm. The reason is that there is a phenomenon of edge collapse in the CNC polishing process, and the edge surface shape has a sudden change that cannot be controlled. Therefore, when walking the polishing track, the polishing head moves a little further outside the lens to reduce the edge collapse phenomenon.

[0078] The size of the polishing head is one-third of the set lens diameter, and the polishing leather is gray GR-35 polyurethane polishing leather; the polishing liquid flow rate is adjusted to the maximum and sprayed on the center of the lens;

[0079] correction is set to -160%; the track-pitch value in path data is 1% of the set lens diameter, i.e. 0.52; the unit of oscillation-time is seconds, and its numerical value is 3 to 5 times the set lens diameter, which is set to 180 in this embodiment; the filter width in extrapolate is 1% of the set lens diameter, i.e. 0.52; the point distance is 1% of the set lens diameter, i.e. 0.52; the target diameter is 48mm; smoothing is performed, and the smoothing value is 2μm; the min.height is set to 0.1μm, and the feed min. value is adjusted to 10mm / min by adjusting the removal-coefficient and oscillation-time values ​​to obtain the final rough polishing program.

[0080] 2. There are two ways to correct astigmatism in the polishing of single-crystal silicon non-spherical surfaces. One is to use the 3D correction software proact provided by the CNC polishing machine to extend the dwell time to eliminate the protruding parts of the surface, but this method is time-consuming. The other method is manual repair, in which the staff polishes the protruding parts of the surface and does not polish the concave parts of the surface.

[0081] Fine polishing: fix the single crystal silicon aspheric lens and its tooling in the CNC polishing machine again, import the second contour model obtained by rough polishing into the CNC polishing machine to calculate the fine polishing program and start fine polishing to obtain a semi-finished product; in actual application, take out the single crystal silicon aspheric lens after fine polishing, drip hand sanitizer on the lens surface while rinsing with pure water, then wipe it with soaked absorbent cotton dipped in hand sanitizer, and finally wipe the surface stains and moisture of the lens with alcohol and citric acid, and then perform contour scanning on the single crystal silicon aspheric lens. If the surface shape is larger than the drawing requirements, repeat fine polishing with the contour model until the surface shape of the semi-finished product is smaller than the drawing requirements, and then enter fine finishing;

[0082] In this embodiment, the following points need to be explained about fine polishing:

[0083] 1. The settings of the CNC polishing machine for fine polishing are as follows:

[0084] The particle size of the polishing liquid selected is 0.5μm; the speed of the polishing head and the workpiece axis of the CNC polishing machine are set to 1000RPM, and the downward pressure is 0.2mm; the lens diameter is set to the actual lens diameter plus 10mm, that is, the lens diameter is set to 52mm; the size of the polishing head is one-third of the set lens diameter, and the orange LP-66 polishing leather is selected.

[0085] The polishing liquid flow rate is adjusted to the maximum and sprayed to the center of the lens; correction is set to -130%; the track-pitch value in path data is 1% of the set lens diameter, that is, 0.52; the unit of oscillation-time is second, and its numerical value is 3 to 5 times the set lens diameter, which is set to 160 in this embodiment; the filterwidth in extrapolate is 1% of the set lens diameter, that is, 0.52; the point distance is 1% of the set lens diameter, that is, 0.52; the target diameter is 48mm; no smoothing is performed; the min.height is set to 0.1μm, and the feed min. value is adjusted to 10mm / min by adjusting the removal-coefficient and oscillation-time values, to obtain the final fine polishing program.

[0086] Fine finishing: transfer the semi-finished product to the grinding and polishing machine for manual finishing; rotate the semi-finished product at a speed of 150RPM, the pressure of the polishing leather on the lens is 2kpa, and the manual finishing is 5 minutes, then drip hand sanitizer onto the lens surface while rinsing with pure water, then wipe it with soaked absorbent cotton dipped in hand sanitizer, and finally wipe the lens clean with alcohol and citric acid. Observe the surface finish. If the surface finish meets the requirements of the drawing, check the surface shape. If the finish does not meet the requirements, repeat the manual finishing process again; if the surface shape is also qualified, the silicon aspheric polishing is completed, and the surface is protected with protective paint to prevent scratches.

[0087] The polishing liquid used in the finishing process is silica sol polishing liquid, and the polishing leather is white wood pulp cotton polishing leather. It should be noted that the area covered by the polishing leather during one rotation of the lens needs to be larger than the surface area of ​​the lens, such as Fig.11 shown.

[0088] In addition, reference Fig.12 In order to improve the processing accuracy, in practical applications, the theoretical indentation is calculated, and the tooling height in the non-CNC polishing machine is adjusted by the difference between the theoretical indentation and the actual indentation to make the theoretical indentation equal to the actual indentation.

[0089] The theoretical indentation is calculated as follows:

[0090]

[0091] Where: L0 = bL e ; we can get L e =2R0b-b 2 / 2R e +2R0-2b;

[0092] Combining the above two equations, we get:

[0093]

[0094] Simplifying, we get:

[0095]

[0096] Among them, R e is the radius of the aspherical surface; R0 is the radius of curvature of the polishing head; b is the amount of downward pressure; Y s is the theoretical indentation diameter.

[0097] Example 2

[0098] refer to Figure 2 , which is basically the same as the process of Example 1, except that the actual lens diameter is 47 mm, and the particle size of the polishing liquid selected is 1 μm, which meets the setting a, so:

[0099] In rough polishing, the rotation speeds of the polishing head and the workpiece axis of the CNC polishing machine are set to 900RPM, and the downward pressure is 0.6mm; the lens diameter is set to the actual lens diameter plus 10mm, that is, the lens diameter is set to 57mm; the track-pitch value in path data is 1% of the set lens diameter, that is, 0.57; the unit of oscillation-time is seconds, and its value is 3 to 5 times the set lens diameter, which is set to 180 in this embodiment; the filter width in extrapolate is 1% of the set lens diameter, that is, 0.57; the point distance is 1% of the set lens diameter, that is, 0.57; the target diameter is 48mm, and the rest remains unchanged.

[0100] In fine polishing, the track-pitch value in path data is 1% of the set lens diameter, that is, 0.57; the unit of oscillation-time is second, and its value is 3 to 5 times the set lens diameter, which is set to 160 in this embodiment; the filter width in extrapolate is 1% of the set lens diameter, that is, 0.57; the point distance is 1% of the set lens diameter, that is, 0.57; the target diameter is 52mm, and the rest remains unchanged.

[0101] Example 3

[0102] The process is basically the same as that of Example 1, except that the actual lens diameter is 148 mm, and the particle size of the selected polishing liquid is 2 μm, which meets the setting d, so:

[0103] In rough polishing, the rotation speed of the polishing head and the workpiece axis of the CNC polishing machine are set to 300RPM, and the downward pressure is 0.4mm; the lens diameter is set to the actual lens diameter plus 10mm, that is, the lens diameter is set to 158mm; the track-pitch value in the path data is 1% of the set lens diameter, that is, 1.58; the unit of oscillation-time is second, and its value is 3 to 5 times the set lens diameter, which is set to 650 in this embodiment; the filterwidth in extrapolate is 1% of the set lens diameter, that is, 1.58; the point distance is 1% of the set lens diameter, that is, 1.58; the target diameter is 145mm, and the rest remains unchanged.

[0104] In fine polishing, the track-pitch value in path data is 1% of the set lens diameter, that is, 1.58; the unit of oscillation-time is second, and its value is 3 to 5 times the set lens diameter, which is set to 620 in this embodiment; the filter width in extrapolate is 1% of the set lens diameter, that is, 1.58; the point distance is 1% of the set lens diameter, that is, 1.58; the target diameter is 145mm, and the rest remains unchanged.

[0105] Example 4

[0106] The process is basically the same as that of Example 3. The effective aperture of the single crystal silicon aspherical lens is 148 mm. The difference is that the particle size of the polishing liquid is 0.5 μm, which meets the setting b. Therefore:

[0107] In the rough polishing, the rotation speed of the polishing head and the workpiece axis of the CNC polishing machine are both set to 500 RPM, the downward pressure is 0.7 mm, and the other settings are the same as those in Example 3.

[0108] Example 5

[0109] refer to Figure 3 , the actual lens diameter is 98 mm; the particle size of the selected polishing liquid is 3 μm, which meets the setting c; the other parameters and steps are the same as those in Example 1.

[0110] Example 6

[0111] refer to Figure 4 , the actual lens diameter is 95 mm; the particle size of the selected polishing liquid is 3 μm, which meets the setting c, except that smoothing is not performed during rough polishing; the remaining parameters and steps are the same as those in Example 5.

[0112] Comparative Example 1

[0113] refer to Figure 5 , the actual lens diameter is 95mm; the particle size of the selected polishing liquid is 2μm, and the speed of the polishing head and the workpiece axis of the CNC polishing machine are both set to 800RPM; the remaining parameters and steps are the same as those in Example 1.

[0114] Comparative Example 2

[0115] refer to Figure 6 , the actual lens diameter is 95mm; the particle size of the polishing liquid selected is 2μm, and the speed of the polishing head and the workpiece axis of the CNC polishing machine are set to 250RPM; the remaining parameters and steps are the same as those in Example 1.

[0116] Comparative Example 3

[0117] refer to Figure 7 , the actual lens diameter is 42mm; the particle size of the polishing liquid selected is 3μm, which meets the setting c, but the pressure is 0.5mm; the other parameters and steps are the same as those in Example 1.

[0118] Comparative Example 4

[0119] Basically the same as Comparative Example 3, but the pressing amount is 0.1 mm.

[0120] Comparative Example 5

[0121] refer to Figure 8 , the actual lens diameter is 95 mm; the particle size of the polishing liquid selected is 3 μm, which meets the setting c; but the correction is set to -60%; the other parameters and steps are the same as those in Example 1.

[0122] Comparative Example 6

[0123] refer to Fig. 9 The actual lens diameter is 95 mm; the particle size of the polishing liquid selected is 3 μm, which meets the setting c; but the orange LP-66 polishing leather is selected for rough polishing; the other parameters and steps are the same as those in Example 1.

[0124] Comparative Example 7

[0125] refer to Fig.10 The actual lens diameter is 47 mm, and milling is used, such as the method disclosed in CN112496876A.

[0126] Result analysis:

[0127] Examples 1 to 6 can all obtain single-crystal silicon aspherical lenses with qualified surface shapes, but the number of repeated rough polishing is different. Figure 4In Example 6, there is occasional mid-frequency error. The reason is that the surface of the milled lens is rough and has many burrs. If it is used directly without smoothing, it will cause a particularly serious mid-frequency error in the first round of rough polishing, making the subsequent process impossible. Therefore, in actual production, it is preferred to perform smoothing to reduce defective products.

[0128] refer to Figure 5 The surface of Example 1 is concave in the middle. The reason is that the rotation speed is too fast, resulting in an irreparable concave in the middle of the lens surface.

[0129] refer to Figure 6 The surface of Example 2 shows "Mercedes-Benz pattern", which is caused by: the rotation speed is too slow and the polishing time is prolonged. In other applications, it is found that if the rough polishing is returned multiple times during the rough polishing process, the same problem will occur.

[0130] refer to Figure 7 , the surface shape of Example 3 is due to the fact that the downward pressure is large. Although the polishing efficiency is high, it brings serious mid-frequency errors. Moreover, due to the large downward pressure, the contact between the lens and the polishing liquid is insufficient, and deep scratches and pits will appear on the surface of the lens.

[0131] The efficiency of Comparative Example 4 is too slow because the pressing amount is small and the polishing time is very long. Considering the economic benefits, it is not suitable for production activities.

[0132] refer to Figure 8 The surface of Example 5 is high and pointed in the middle, and it is speculated that the reason is that the edge residence time is too short.

[0133] refer to Fig. 9 The surface of Example 6 shows "Mercedes-Benz pattern" because the polishing skin is too soft during rough polishing and the high hardness position cannot be removed.

[0134] refer to Fig.10 The surface of the surface of comparative example 7 has many burrs, which is presumably due to the wear of the diamond tool.

[0135] Although the embodiments of the present application have been shown and described, those skilled in the art will appreciate that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present application, and that the scope of the present application is defined by the claims and their equivalents.

Claims

1. A CNC polishing process for a single crystal silicon aspheric lens, characterized in that: The steps include: Step 1: Scan the profile of the single crystal silicon aspheric lens to obtain a profile model; Step 2: Fix the single crystal silicon aspheric lens and its tooling in the CNC polishing machine, import the contour model into the CNC polishing machine to calculate the rough polishing program and start rough polishing; Step 3: Perform profile scanning on the single crystal silicon aspheric lens after rough polishing to obtain a new profile model; If the PV of the surface is greater than the drawing requirements, return to step 2; if the PV of the surface is less than the drawing requirements, go to step 4; Step 4: Fix the single crystal silicon aspheric lens and its tooling in the CNC polishing machine again, and import the contour model obtained in step 3 into the CNC polishing machine to calculate the fine polishing program and start fine polishing to obtain a semi-finished product; Step 5: Refine the semi-finished product to obtain the finished product; Among them, the settings of the CNC polishing machine meet the following conditions: Setting a: When the lens diameter is set to be less than 150 mm and the particle size of the polishing liquid is 0.5 to 1 μm, the speed of the polishing head and the workpiece axis of the CNC polishing machine are set to 800 to 1000 RPM, and the downward pressure is 0.5 to 0.7 mm; Setting b: When the lens diameter is set to be greater than 150 mm and the particle size of the polishing liquid is 0.5 to 1 μm, the speed of the polishing head and the workpiece axis of the CNC polishing machine is set to 300 to 500 RPM, and the downward pressure is 0.5 to 0.7 mm; Setting c: When the lens diameter is set to be less than 150 mm and the particle size of the polishing liquid is 2 to 3 μm, the speed of the polishing head and the workpiece axis of the CNC polishing machine is set to 300 to 500 RPM, and the downward pressure is 0.2 to 0.4 mm; Setting d: When the lens diameter is set to be greater than 150 mm and the particle size of the polishing liquid is 2 to 3 μm, the speed of the polishing head and the workpiece axis of the CNC polishing machine are set to 150 to 300 RPM, and the downward pressure is 0.2 to 0.4 mm.

2. The CNC polishing process for a single crystal silicon aspheric lens according to claim 1, characterized in that: In step 3, if the PV of the surface shape is greater than the requirements of the drawing, first determine whether the single crystal silicon aspherical lens is astigmatic based on the contour model; If yes, perform astigmatism correction and return to step 3; if no, return to step 2.

3. The CNC polishing process for a single crystal silicon aspheric lens according to claim 1, characterized in that: The polishing liquid in step 2 is a mixture of diamond powder, aluminum oxide, silicon dioxide, oily suspension and pure water in a ratio of 2:1:2:6:29; the polishing head in step 2 adopts a polishing leather made of polyurethane material.

4. The CNC polishing process for a single crystal silicon aspheric lens according to claim 1, characterized in that: The remaining settings of the CNC polishing machine in step 2 are as follows: Set the lens diameter to the actual lens diameter + 5 to 10 mm; Correction is set to -130% to -180%; The track-pitch value in the path data is one percent of the set lens diameter; The unit of oscillation-time is seconds, and its value is 3 to 5 times the set lens diameter; The filter width in extrapolate is 1% of the set lens diameter, the point distance is 1% of the set lens diameter, and the target diameter is the effective diameter plus 5 to 10 mm; Smoothing is performed, and the smoothing value is 2 to 3 μm; Set the min.height to 0-0.2 μm, adjust the removal-coefficient and oscillation-time values, and adjust the feed min. value to 10 mm / min.

5. The CNC polishing process for a single crystal silicon aspheric lens according to claim 1, characterized in that: The settings of the CNC polishing machine in step 4 are as follows: The particle size of the polishing liquid is 0.5-1μm, the downward pressure is 0.1-0.2mm, and the other setting requirements are the same as rough polishing.

6. The CNC polishing process for a single crystal silicon aspheric lens according to claim 1, characterized in that: In step 5, the semi-finished product is transferred to a grinding and polishing machine, and the semi-finished product is rotated at a speed of 100 to 200 RPM, and then the semi-finished product is finely polished with a polishing leather at a pressure of 2 to 4 kPa.

7. The CNC polishing process for a single crystal silicon aspheric lens according to claim 1, characterized in that: Before step 1, a single-crystal silicon aspheric lens with a surface type PV≤2 μm is prepared by milling, and sharp edges at the edges of the single-crystal silicon aspheric lens are removed.

8. The CNC polishing process for a single crystal silicon aspheric lens according to claim 1, characterized in that: The size of the polishing head is one third to one quarter of the diameter of the set lens.

9. The CNC polishing process for a single crystal silicon aspheric lens according to claim 1, characterized in that: In the step 2, the actual indentation diameter is compared with the theoretical calculated indentation size, and the rough polishing tool height is adjusted according to the difference to make the theoretical indentation equal to the actual indentation size.

10. A single crystal silicon aspheric lens, wherein the diameter of the single crystal silicon aspheric lens is less than 320 mm, characterized in that: The aspherical lens is manufactured by the CNC polishing process of the single crystal silicon aspherical lens as described in any one of claims 1 to 9.

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