Monocrystalline silicon aspherical lens and numerical control polishing process thereof

Abstract

The application relates to the technical field of optical processing, and provides a single-crystal silicon aspheric lens and a numerical control polishing process thereof, which is carried out by using a numerical control polishing machine, comprises main steps of rough polishing, fine polishing and finishing, and process parameters are adjusted according to the characteristics of single-crystal silicon, so that the single-crystal silicon aspheric lens with a diameter of less than 320 mm can be polished, the front surface PV of the single-crystal silicon aspheric lens can be less than 0.3 microns by means of the numerical control polishing machine, and the surface smoothness reaches 40 / 20. The single-crystal silicon aspheric lens with a diameter of more than 320 mm also has reference significance.

Description

Technical Field

[0001] This application relates to the field of optical processing technology, specifically to a single-crystal silicon aspherical lens and its CNC polishing process. Background Technology

[0002] Aspherical lenses come in shapes including parabolic, quadratic, cubic, or higher-order curves. During the design process, these lenses fully consider correction factors such as aberrations, chromatic aberration, and spherical aberration. Typically, a single aspherical lens can achieve the corrective effect of multiple spherical lenses, thus reducing the number of lenses required. This not only improves the lens's precision and sharpness but also enhances the accuracy of color reproduction, while reducing internal light reflection and minimizing lens size. Aspherical lenses also feature high zoom capabilities, short object distances, and large apertures. High zoom simplifies lens design, short object distances are suitable for close-up shooting, and large apertures provide excellent performance in low-light conditions. These advantages have led to the increasingly widespread application of aspherical lenses.

[0003] Monocrystalline silicon is widely used in infrared optics due to its advantages such as low density, high hardness, high transmittance, low self-emission, and low cost. Although the high hardness of monocrystalline silicon brings good performance, its processing difficulty means that grinding and polishing techniques are still used to produce spherical lenses in most cases in the infrared field.

[0004] In recent years, with increased recognition of the superior performance of aspherical lenses, many infrared optics designers have begun to explore designing silicon lenses as aspherical lenses. However, the production of monocrystalline silicon aspherical lenses remains a significant challenge for companies. Currently, monocrystalline silicon aspherical lenses with a diameter of less than 30mm can be machined using ultra-precision single-point lathes, such as the ultra-precision turning method for silicon lens aspherical surfaces disclosed in CN112496876A. However, due to the Mohs hardness of silicon reaching 7, diamond tools are prone to wear, leading to frequent tool replacements and increased production costs. Furthermore, the surface produced by single-point turning often exhibits "rainbow patterns" and the "Mercedes-Benz pattern" characteristic of monocrystalline silicon, resulting in poor surface finish.

[0005] CN110682185A discloses a high-precision exposure lens processing method for pulse compression grating fabrication, including the construction of a self-collimating interferometric detection device, milling, polishing, precision polishing, and smoothing of the aspherical surface of the exposure lens. This improves the wavefront quality across the entire frequency band at the exposure wavelength. However, it is not applicable to the production of aspherical lenses made of all materials, especially for the production of monocrystalline silicon aspherical lenses, because monocrystalline silicon aspherical lenses exhibit varying hardness in different directions, with higher hardness at the center and lower hardness at the edges. Summary of the Invention

[0006] To address the aforementioned technical problems, this application provides a CNC polishing process for monocrystalline silicon aspherical lenses. This polishing process can polish monocrystalline silicon aspherical lenses with a diameter of less than 320mm. With the aid of a CNC polishing machine, the PV of the optimized front profile can be reduced to below 0.3μm, and the surface finish can reach 40 / 20. This process is also of reference value for monocrystalline silicon aspherical lenses with a diameter of more than 320mm.

[0007] The technical solution of this application is:

[0008] A CNC polishing process for monocrystalline silicon aspherical lenses includes the following steps:

[0009] Step 1: Perform contour scanning on the monocrystalline silicon aspherical lens to obtain the contour model;

[0010] Step 2: Fix the monocrystalline silicon aspherical lens and its tooling inside the CNC polishing machine, import the contour model into the CNC polishing machine to calculate the rough polishing program and start the rough polishing;

[0011] Step 3: Perform contour scanning on the rough-polished monocrystalline silicon aspherical lens to obtain a new contour model;

[0012] If the PV of its face is greater than the drawing requirement, return to step 2; if the PV of its face is less than the drawing requirement, proceed to step 4.

[0013] Step 4: Fix the monocrystalline silicon aspherical lens and its tooling back into the CNC polishing machine, 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] The settings of the CNC polishing machine must meet the following conditions:

[0016] Setting a) When the lens diameter is less than 150mm and the polishing fluid particle size is 0.5~1μm, set the rotation speed of the polishing head and the workpiece axis of the CNC polishing machine to 800~1000RPM and the downward pressure to 0.5~0.7mm.

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

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

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

[0020] In practical applications, this application adjusts the setting parameters of the CNC polishing machine according to the lens and polishing fluid to avoid the CNC polishing machine damaging the monocrystalline silicon aspherical lens and causing irreparable defects, and can also reduce intermediate frequency errors.

[0021] In the above-mentioned CNC polishing process of monocrystalline silicon aspherical lenses, if the PV of the surface shape is greater than the drawing requirements in step 3, the aspherical lens is first judged to be astigmatic based on the contour model.

[0022] If yes, perform astigmatism correction and return to step 3; otherwise, return to step 2.

[0023] In the above-mentioned CNC polishing process for monocrystalline silicon aspherical lenses, the polishing fluid in step 2 is a mixture of diamond powder, alumina, silica, oily suspending agent, and pure water, in a ratio of 2:1:2:6:29; the polishing head in step 2 uses a polishing skin made of polyurethane material.

[0024] In the above-described CNC polishing process for monocrystalline silicon aspherical lenses, 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. This is because the CNC polishing process has an edge collapse phenomenon, and the surface shape of the edge has abrupt changes that cannot be controlled. Therefore, when following the polishing trajectory, the polishing head moves a certain distance outward from the lens, which can reduce the edge collapse phenomenon.

[0026] The correction is set to -130% to -180%.

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

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

[0029] In extrapolate, the filter width is set to 1 / 100 of the lens diameter, the point distance is set to 1 / 100 of the lens diameter, and the target diameter is the effective aperture plus 5-10mm.

[0030] Perform a smoothing process with a smoothing value of 2–3 μm.

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

[0032] In the above-mentioned CNC polishing process for monocrystalline silicon aspherical lenses, the settings of the CNC polishing machine in step 4 are as follows:

[0033] The polishing slurry particle size is 0.5–1 μm, the pressure is 0.1–0.2 mm, and the other settings are the same as for coarse polishing.

[0034] In the above-mentioned CNC polishing process for monocrystalline silicon aspherical lenses, step 5 involves transferring the semi-finished product to a polishing machine and rotating it at a speed of 100-200 RPM. Then, a polishing pad is used to refine the semi-finished product under a pressure of 2-4 kPa.

[0035] In the above-mentioned CNC polishing process of monocrystalline silicon aspherical lenses, before step 1, a monocrystalline silicon aspherical lens with a surface area PV≤2μm is prepared by milling, and the sharp edges at the edges of the monocrystalline silicon aspherical lens are removed.

[0036] In the above-mentioned CNC polishing process for monocrystalline silicon aspherical lenses, 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 monocrystalline silicon aspherical lenses, in step 2, the actual indentation diameter is compared with the theoretically calculated indentation size, and the height of the rough polishing fixture is adjusted according to the difference to make the theoretical indentation size equal to the actual indentation size.

[0038] This application also discloses a monocrystalline silicon aspherical lens with a diameter of less than 320 mm, which is manufactured using the aforementioned CNC polishing process for monocrystalline silicon aspherical lenses. Its global surface area (PV) reaches less than 0.3 micrometers, and its surface finish reaches 40 / 20.

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

[0040] The polishing process described in this application can polish monocrystalline silicon aspherical lenses with a diameter of less than 320mm. With the help of a CNC polishing machine, the PV of the optimized front face can be reduced to less than 0.3μm, and the surface finish can reach 40 / 20.

[0041] Meanwhile, compared to single-point turning, polishing can overcome the problems of "rainbow patterns" and "Mercedes patterns" on the surface caused by single-point turning, and it is more efficient and less expensive.

[0042] Furthermore, this application can also control the stability of the polished surface more precisely by controlling the amount of downward pressure. Attached image description:

[0043] Figure 1 This is an optical surface pattern of the aspherical lens obtained in Embodiment 1 of the present invention;

[0044] Figure 2 This is an optical surface pattern of the aspherical lens obtained in Embodiment 2 of the present invention;

[0045] Figure 3 This is an optical surface pattern of the aspherical lens obtained in Embodiment 5 of the present invention;

[0046] Figure 4 This is an optical surface pattern of the aspherical lens obtained in Embodiment 6 of the present invention;

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

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

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

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

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

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

[0053] Figure 11 This is a schematic diagram illustrating the interaction between the polishing head and the lens during the finishing process of this invention.

[0054] Figure 12 This is a schematic diagram of the computational theory of indentation according to the present invention.

[0055] Figure 13 This is a simplified flowchart of the processing flow of the present invention.

[0056] Explanation of reference numerals in the attached figures:

[0057] 1. Polishing head; 2. Lens. Detailed Implementation

[0058] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

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

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

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

[0062] Example 1

[0063] refer to Figure 1 A CNC polishing process for monocrystalline silicon aspherical lenses, in this embodiment, the actual diameter of the monocrystalline silicon aspherical lens is 42mm, and its composition includes a mixed solution of diamond powder, alumina, silicon dioxide, an oily suspending agent, and pure water, prepared in a ratio of 2:1:2:6:29; Figure 13 As shown, it includes the following steps:

[0064] Milling: A CNC milling machine is used to adjust the surface profile of the monocrystalline silicon aspherical lens to below 2μm. Otherwise, medium- and high-frequency surface profile errors will occur during polishing, making it difficult to control the polished surface profile to below 0.5μm. It is also necessary to chamfer or grind the edges with sandpaper to remove sharp edges and prevent damage to the polished skin.

[0065] Contour scanning: A contour scan is performed on a single-crystal silicon aspherical lens with a face size ≤2μm to obtain the first contour model;

[0066] Rough polishing: Fix the monocrystalline silicon aspherical lens and its tooling inside the CNC polishing machine, import the first contour model into the CNC polishing machine to calculate the rough polishing program and start the rough polishing;

[0067] Contour scanning: A contour scan is performed on the rough-polished monocrystalline silicon aspherical lens to obtain a second contour model; and the subsequent processing flow is determined based on the surface shape of the second contour model. The determination process is as follows:

[0068] When the PV of its surface is less than that required by the drawing, proceed to fine polishing;

[0069] When the PV of its surface is greater than the drawing requirements, first observe whether the outline model has astigmatism. The reason is that the hardness of single crystal silicon has the characteristics of different directions and anisotropy, and the removal efficiency is different in different places, which easily produces astigmatism and deformation.

[0070] If astigmatism exists, astigmatism correction is performed, and contour scanning is performed again after astigmatism correction.

[0071] If no astigmatism exists, the coarse polishing procedure is recalculated using the second contour model, and coarse polishing is performed again.

[0072] Repeat the above judgment process until the surface shape of the monocrystalline silicon aspherical lens is smaller than the drawing requirements, then proceed to fine polishing.

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

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

[0075] The selected polishing slurry has a particle size of 3μm and meets the setting c because the lens diameter is set to be less than 150mm;

[0076] Therefore, the rotation speed of both the polishing head and the workpiece axis of the CNC polishing machine is set to 400 RPM and the rotation direction of the polishing head and the workpiece axis is the same, with a downward pressure of 0.2 mm.

[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 the CNC polishing process has an edge collapse phenomenon, and the surface shape of the edge has abrupt changes that cannot be controlled. Therefore, when following the polishing trajectory, the polishing head moves a little further out of the lens, which can reduce the edge collapse phenomenon.

[0078] The polishing head should be one-third the size of the lens diameter, and the polishing pad should be gray GR-35 polyurethane polishing pad. The polishing fluid flow rate should be set to maximum and sprayed towards the center of the lens.

[0079] The correction is set to -160%; the track-pitch value in the path data is one-hundredth of the set lens diameter, i.e., 0.52; the oscillation-time is in 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 one-hundredth of the set lens diameter, i.e., 0.52; the point distance is one-hundredth of the set lens diameter, i.e., 0.52; the target diameter is 48mm; a smooth value of 2μm is applied; 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 coarse polishing procedure.

[0080] 2. There are two methods for correcting astigmatism during aspheric polishing of monocrystalline silicon. One method is to use the 3D correction software Proact on the CNC polishing machine to extend the dwell time on the protruding parts of the surface to eliminate them, but this method is time-consuming. The other method is manual correction, where the operator polishes the protruding parts of the surface, leaving the concave parts unpolished.

[0081] Fine polishing: The monocrystalline silicon aspherical lens and its fixture are fixed again in the CNC polishing machine, and the second contour model obtained from rough polishing is imported into the CNC polishing machine to calculate the fine polishing program and start fine polishing to obtain a semi-finished product. In practical applications, after fine polishing, the monocrystalline silicon aspherical lens is taken out, and while dripping hand soap onto the lens surface, it is rinsed with pure water, then wiped with a damp cotton ball soaked in hand soap, and finally wiped clean of surface dirt and moisture with alcohol and citric acid. Then, the contour of the monocrystalline silicon aspherical lens is scanned. If the surface shape is larger than the drawing requirements, the fine polishing is repeated with the contour model until the surface shape of the semi-finished product is smaller than the drawing requirements, and then it enters the finishing stage.

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

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

[0084] The selected polishing slurry has a particle size of 0.5μm; the rotation speed of the polishing head and the workpiece axis of the CNC polishing machine are both 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 set lens diameter value is 52mm; the size of the polishing head is one-third of the set lens diameter, and the polishing skin is orange LP-66 polishing skin.

[0085] The polishing fluid flow rate is set to maximum and sprayed onto the center of the lens; the correction is set to -130%; the track-pitch value in the path data is one-hundredth of the set lens diameter, i.e., 0.52; the oscillation-time is in seconds, and its value is 3 to 5 times the set lens diameter, set to 160 in this embodiment; the filterwidth in extrapolate is one-hundredth of the set lens diameter, i.e., 0.52; the point distance is one-hundredth of the set lens diameter, i.e., 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 procedure.

[0086] Fine finishing: Transfer the semi-finished product to the polishing machine for manual finishing. Rotate the semi-finished product at 150 RPM, with the polishing skin applying 2 kPa pressure to the lens, for 5 minutes. Then, while dripping hand soap onto the lens surface, rinse with pure water, wipe with a damp cotton ball soaked in hand soap, and finally clean the lens with alcohol and citric acid. Observe the surface smoothness. If the surface smoothness meets the drawing requirements, check the surface shape. If the smoothness does not meet the requirements, repeat the manual finishing process. If the surface shape is also qualified, the silicon aspherical polishing is complete. Apply a protective varnish to the surface to prevent scratches.

[0087] The polishing solution used in the fine-tuning process is a silica sol polishing solution, and the polishing pad is a white wood pulp cotton polishing pad. It is important to note that the area covered by the polishing pad in one rotation of the lens needs to be larger than the surface area of ​​the lens. Figure 11 As shown.

[0088] In addition, refer to Figure 12 In order to improve the machining 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 so that the theoretical indentation and the actual indentation are equal in size.

[0089] The theoretical indentation calculation method is as follows:

[0090]

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

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

[0093]

[0094] Simplifying, we get:

[0095]

[0096] Among them, R e R0 is the radius of the aspherical surface; R0 is the radius of curvature of the polishing head; b is the downward pressure; Y0 s This is the theoretical indentation diameter.

[0097] Example 2

[0098] refer to Figure 2 The process is basically the same as in Example 1, except that the actual lens diameter is 47mm and the polishing slurry particle size is 1μm, which meets the setting a. Therefore:

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

[0100] In fine polishing, the track-pitch value in the path data is one-hundredth of the set lens diameter, i.e., 0.57; the oscillation-time is in seconds, 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 one-hundredth of the set lens diameter, i.e., 0.57; the point distance is one-hundredth of the set lens diameter, i.e., 0.57; the target diameter is 52mm, and the rest remain unchanged.

[0101] Example 3

[0102] The process is basically the same as in Example 1, except that the actual lens diameter is 148mm and the polishing slurry particle size is 2μm, which meets the set d. Therefore:

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

[0104] In fine polishing, the track-pitch value in the path data is one-hundredth of the set lens diameter, i.e., 1.58; the oscillation-time is in seconds, 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 one-hundredth of the set lens diameter, i.e., 1.58; the point distance is one-hundredth of the set lens diameter, i.e., 1.58; the target diameter is 145mm, and the rest remain unchanged.

[0105] Example 4

[0106] The process is basically the same as in Example 3, with the effective aperture of the monocrystalline silicon aspherical lens being 148mm. The difference lies in the particle size of the polishing slurry used, which is 0.5μm, conforming to 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 in Example 3.

[0108] Example 5

[0109] refer to Figure 3 The actual lens diameter is 98mm; the particle size of the polishing fluid used is 3μm, which meets the set c; the remaining parameters and steps are the same as in Example 1.

[0110] Example 6

[0111] refer to Figure 4 The actual lens diameter is 95mm; the particle size of the polishing liquid used is 3μm, which meets the set c. The difference is that smoothing was not performed during rough polishing; the other parameters and steps are the same as in Example 5.

[0112] Comparative Example 1

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

[0114] Comparative Example 2

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

[0116] Comparative Example 3

[0117] refer to Figure 7 The actual lens diameter is 42mm; the selected polishing fluid has a particle size of 3μm, which meets the set c, but the pressure is 0.5mm; the remaining parameters and steps are the same as in Example 1.

[0118] Comparative Example 4

[0119] It is basically the same as Comparative Example 3, but the downward pressure is 0.1mm.

[0120] Comparative Example 5

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

[0122] Comparative Example 6

[0123] refer to Figure 9 The actual lens diameter is 95mm; the selected polishing fluid has a particle size of 3μm, which meets the set c; however, orange LP-66 polishing skin is used for coarse polishing; the remaining parameters and steps are the same as in Example 1.

[0124] Comparative Example 7

[0125] refer to Figure 10 The actual lens diameter is 47mm, and it is milled, as disclosed in CN112496876A.

[0126] Results analysis:

[0127] Examples 1-6 all yielded monocrystalline silicon aspherical lenses with acceptable surface shapes, differing only in the number of repeated coarse polishing steps. Figure 4In Example 6, mid-frequency errors occasionally occur because the surface of the milled lens has many burrs and is relatively rough. If it is used directly without smoothing, it will cause particularly serious mid-frequency errors in the first round of rough polishing, making subsequent processes impossible. Therefore, in actual production, it is preferable to perform smoothing to reduce defective products.

[0128] refer to Figure 5 The reason why the lens surface in Comparative Example 1 is concave in the middle is that the excessive rotation speed causes an irreparable concavity in the middle surface of the lens.

[0129] refer to Figure 6 The surface of Comparative Example 2 exhibits "Mercedes-Benz patterns" because the rotation speed is too slow, resulting in a longer polishing time. In other applications, it was found that repeatedly returning to the rough polishing stage during the initial rough polishing process also produces the same problem.

[0130] refer to Figure 7 The reason for the surface shape of Comparative Example 3 is that the downward pressure is large. Although the polishing efficiency is high, it brings serious mid-frequency error. Moreover, due to the large downward pressure, the lens does not have sufficient contact with the polishing fluid, 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 pressure is small and the polishing time is long. Considering economic benefits, it is not suitable for production activities.

[0132] refer to Figure 8 The face of Comparative Example 5 is high and pointed in the middle, presumably because the edge stays too short.

[0133] refer to Figure 9 The reason why the surface of Comparison 6 shows "Mercedes-Benz pattern" is that the polishing skin in the rough polishing is too soft and cannot remove the hard areas.

[0134] refer to Figure 10 The surface of Comparative Example 7 has many burrs, presumably due to wear on the diamond tool.

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

Claims

1. A CNC polishing process for monocrystalline silicon aspherical lenses, characterized in that, Includes the following steps: Step 1: Perform contour scanning on the monocrystalline silicon aspherical lens to obtain the contour model; Step 2: Fix the monocrystalline silicon aspherical lens and its tooling inside the CNC polishing machine, import the contour model into the CNC polishing machine to calculate the rough polishing program and start the rough polishing; Step 3: Perform contour scanning on the rough-polished monocrystalline silicon aspherical lens to obtain a new contour model; If the PV of its face is greater than the drawing requirement, return to step 2; if the PV of its face is less than the drawing requirement, proceed to step 4. Step 4: Fix the monocrystalline silicon aspherical lens and its tooling back into the CNC polishing machine, 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; The settings of the CNC polishing machine must meet the following conditions: Setting a) When the lens diameter is less than 150mm and the polishing fluid particle size is 0.5~1μm, set the rotation speed of the polishing head and the workpiece axis of the CNC polishing machine to 800~1000RPM and the downward pressure to 0.5~0.7mm. Setting b: When the lens diameter is greater than 150mm and the polishing slurry particle size is 0.5~1μm, set the rotation speed of the polishing head and the workpiece axis of the CNC polishing machine to 300~500RPM and the downward pressure to 0.5~0.7mm. Setting c: When the lens diameter is less than 150mm and the polishing slurry particle size is 2~3μm, set the rotation speed of the polishing head and the workpiece axis of the CNC polishing machine to 300~500RPM and the downward pressure to 0.2~0.4mm. Setting d: When the lens diameter is greater than 150mm and the polishing fluid particle size is 2~3μm, set the rotation speed of the polishing head and the workpiece axis of the CNC polishing machine to 150~300RPM and the downward pressure to 0.2~0.4mm.

2. The CNC polishing process for monocrystalline silicon aspherical lenses according to claim 1, characterized in that, If the PV of the surface shape is greater than the drawing requirements in step 3, first determine whether the monocrystalline silicon aspherical lens has astigmatism based on the contour model. If yes, perform astigmatism correction and return to step 3; otherwise, return to step 2.

3. The CNC polishing process for monocrystalline silicon aspherical lenses according to claim 1, characterized in that, The polishing fluid in step 2 is a mixture of diamond powder, alumina, silica, oily suspending agent, and pure water, in a ratio of 2:1:2:6:29; the polishing head in step 2 uses a polishing skin made of polyurethane material.

4. The CNC polishing process for monocrystalline silicon aspherical lenses according to claim 1, characterized in that, The remaining settings for the CNC polishing machine in step 2 are as follows: Set the lens diameter to the actual lens diameter + 5~10mm; The edge dwell rate is set to -130% to -180%. The pitch is one-hundredth of the set lens diameter; The time required for one round of polishing is measured in seconds, and its value is 3 to 5 times the set lens diameter; The sampling pitch is one-hundredth of the set lens diameter, the sampling point distance is one-hundredth of the set lens diameter, and the target diameter is the effective aperture plus 5~10mm; Smoothing is performed, with the smoothing value being 2~3μm; Set the removal amount to 0~0.2μm, adjust the dwell time and the time required for one round of polishing, and adjust the minimum value of the polishing head movement speed to 10mm / min.

5. The CNC polishing process for monocrystalline silicon aspherical lenses according to claim 1, characterized in that, The settings for the CNC polishing machine in step 4 are as follows: The polishing slurry has a particle size of 0.5~1μm and a pressure of 0.1~0.2mm. The other settings are the same as for coarse polishing.

6. The CNC polishing process for monocrystalline silicon aspherical lenses according to claim 1, characterized in that, In step 5, the semi-finished product is transferred to a polishing machine and rotated at a speed of 100-200 RPM. Then, a polishing pad is used to refine the semi-finished product under a pressure of 2-4 kPa.

7. The CNC polishing process for monocrystalline silicon aspherical lenses according to claim 1, characterized in that, Before step 1, a monocrystalline silicon aspherical lens with a surface area PV ≤ 2μm is prepared by milling, and the sharp edges at the edges of the monocrystalline silicon aspherical lens are removed.

8. The CNC polishing process for monocrystalline silicon aspherical lenses 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 monocrystalline silicon aspherical lenses according to claim 1, characterized in that, In step 2, the actual indentation diameter is compared with the theoretically calculated indentation size, and the height of the rough polishing tool is adjusted according to the difference to make the theoretical indentation size equal to the actual indentation size.

10. A monocrystalline silicon aspherical lens, wherein the diameter of the monocrystalline silicon aspherical lens is 320 mm or less, characterized in that, It is prepared by CNC polishing process of single-crystal silicon aspherical lens as described in any one of claims 1 to 9.

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