Large-size optical flat parallelism fine-tuning method

Abstract

This invention relates to a method for refining the parallelism of large-size optical flats, belonging to the field of precision machining of optical planar components. By using a goniometer combined with the breath test to accurately determine the thin and thick ends of the planar components and control related process parameters, the parallelism level of optical flats is significantly improved. The parallelism of optical flats is increased from θ≤10″ to a higher level of θ=1″~2″. The flat refining cycle is reduced from the original 8 hours to the current 2~3 hours, and the first-pass yield rate is increased from less than 10% to more than 80%.

Description

Technical Field

[0001] This invention relates to the field of precision machining technology for optical planar elements, and in particular to a method for refining the parallelism of large-size optical flats. Background Technology

[0002] An optical flat is a circular measuring tool made of optical glass, with two highly precise planes on its top and bottom surfaces, some of which exhibit high parallelism. Utilizing the principle of light wave interference, it is used to inspect the flatness and parallelism of the measuring surfaces of gauge blocks and precision measuring tools (or precision workpieces). It can also be used to compare the measured block or tool with a standard block to determine its parallelism error. Additionally, optical flats can be used as tools to inspect the adjustment and quality of laser beam expanders.

[0003] Traditional optical flat wafer manufacturing methods (for diameters < φ130mm, a wafer-level processing method is used; for diameters ≥ φ130mm, a single-piece processing method is used). Taking the single-piece processing method as an example, the part processing flow is as follows: fine grinding and polishing of the first surface → fine grinding of the second surface to control the edge thickness difference of the part, using a micrometer to check the edge thickness difference. When the measured value is ≤ 0.002mm, the second surface polishing begins → cleaning and self-inspection → if it is unqualified, the edge thickness difference of the part needs to be measured again with a micrometer, and the thick end of the part is subjected to a load for rework until the parallelism of the part passes the self-inspection.

[0004] It is worth noting that traditional machining methods use micrometers to determine the thickness of parts, with a minimum division value of 0.01mm. The estimated value can be 0.002 to 0.003mm. Taking a part with a diameter of φ130mm and an estimated error of 0.002mm as an example, the angular error is converted to arctan(0.002 / 130) = 3.2″. That is, the highest parallelism accuracy of this method is 3″, and the conventional machining accuracy is 10″, which cannot meet the required 1″ to 2″. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a method for refining the parallelism of large-size optical flats, in order to solve the problems that the parallelism of existing optical flat processing technology cannot reach 1″ to 2″, and that the processing time is long and the yield is low.

[0006] On one hand, embodiments of the present invention provide a method for refining the parallelism of large-size optical flats, the method comprising the following steps:

[0007] Check the parallelism of the flat crystal. For flat crystals that meet the parallelism requirements, take a certain plane of the flat crystal that meets the process requirements before fine finishing as the reference plane. If there is no plane that meets the process requirements before fine finishing, use a ring polisher to polish any plane of the flat crystal until it meets the process requirements before fine finishing and take it as the reference plane.

[0008] Based on the reference plane of the flat crystal, check whether the parallelism of the flat crystal meets the parallelism requirements; if it meets the requirements, proceed with the following steps:

[0009] Check and confirm whether the condition of the ring polishing die on the ring polishing machine meets the process requirements before fine repair. If it does not meet the process requirements before fine repair, then repair the ring polishing die until it meets the process requirements.

[0010] Use a goniometer to observe and determine the thin and thick ends of the flat crystal;

[0011] The flat crystal is precision-finished using a ring polishing machine.

[0012] Based on further improvements to the above method, the pre-finishing process requirements for the flat crystal include a surface aperture ≤ 0.5, a local aperture ≤ 0.2, and a flat crystal parallelism ≤ 20″.

[0013] Based on further improvements to the above method, the pre-finishing process requirements corresponding to the flat crystal also include the pre-finishing process requirements corresponding to the ring polishing die, which means that the flat crystal surface processed by the ring polishing die has an aperture ≤ 0.5 and a local aperture ≤ 0.2.

[0014] Based on a further improvement of the above method, the trimming of the ring polishing die includes:

[0015] When the aperture of the ring polishing die is greater than 0.5, the position of the ring polishing correction disk is adjusted by moving it.

[0016] When the local aperture is greater than 0.2, use a hacksaw blade to draw square grooves on the ring polishing die, and at the same time use a scraper to make "×" marks on each square to make it more refined.

[0017] Based on a further improvement of the above method, the process of using a goniometer to observe and determine the thickness of the flat crystal is as follows:

[0018] Place the flat crystal on a horizontal plane and align the observation surface of the goniometer objective lens with the surface of the flat crystal.

[0019] Rotate the flat crystal about the central axis perpendicular to the surface of the flat crystal, and observe the images of the upper and lower surfaces using a goniometer;

[0020] The flat crystal is rotated until the upper and lower surfaces coincide in the Y-axis direction, then the rotation stops;

[0021] Breathe on the lower surface of the optical flat, and the image of the lower surface of the optical flat will darken. Observe the upper and lower surface images of the optical flat to determine the position of the thin and thick ends.

[0022] Based on a further improvement of the above method, when the lower surface image of the flat crystal is located above the upper surface image, the thick end of the flat crystal is at the bottom.

[0023] Based on a further improvement of the above method, the fine finishing of the flat crystal specifically involves placing the flat crystal in a ring polisher with a surface shape that meets the requirements, and fine finishing the processed surface of the flat crystal according to preset parameters.

[0024] Based on a further improvement of the above method, the preset parameters include

[0025] The softening point of the asphalt mold for the ring polisher is 64 degrees Celsius when 60# and 65# asphalt are mixed in a 1:4 ratio.

[0026] Ambient temperature: 22℃~24℃;

[0027] Temperature gradient: <1℃ / h;

[0028] Relative humidity: 30%–70%;

[0029] Equipment rotation speed: 2-3 r / min;

[0030] Polishing powder concentration: 0.3%–0.5%;

[0031] Polishing powder flow rate: 0.8~1.0l / h;

[0032] Processing time: Check every 2-3 hours;

[0033] Select an appropriate load to hold down the thick end of the flat crystal during the finishing process.

[0034] Based on a further improvement of the above method, the appropriate load is calculated according to the correspondence between the change in parallelism Δθ of the flat crystal, the repair time t of the flat crystal, and the diameter D of the flat crystal. The result is then rounded up and expressed as a formula:

[0035] M=ceil(Δθ·D 2 / (184000·t)), where ceil represents rounding up.

[0036] Based on further improvements to the above method, the parallelism range of the refined flat crystal is 1″ to 2″.

[0037] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0038] 1. This invention is applicable to the precision polishing of optical planar elements, which can improve the parallelism level of optical planar elements and significantly reduce the difficulty of parallelism control of high-precision planar elements.

[0039] 2. This invention significantly improves the parallelism grade of optical flats, increasing the parallelism θ≤10″ to θ=1″~2″, reducing the precision repair cycle of optical flats from the original 8h to 2~3h, and increasing the first-pass yield rate from less than 10% to more than 80%.

[0040] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0041] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0042] Figure 1 This is a process flow diagram of the present invention.

[0043] Figure 2 This is a schematic diagram of the goniometer of the present invention displaying images of the upper and lower surfaces of the optical plane.

[0044] Figure 3 This is a schematic diagram of the pressure load on the thick end of the flat crystal during the flat crystal parallelism fine-tuning process of the present invention. Detailed Implementation

[0045] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0046] A specific embodiment of the present invention discloses a method for refining the parallelism of large-size optical flats, the method comprising the following steps:

[0047] Check the parallelism of the flat crystal. For flat crystals that meet the parallelism requirements, take a certain plane of the flat crystal that meets the process requirements before fine finishing as the reference plane. If there is no plane that meets the process requirements before fine finishing, use a ring polisher to polish any plane of the flat crystal until it meets the process requirements before fine finishing and take it as the reference plane.

[0048] Based on the reference plane of the flat crystal, check whether the parallelism of the flat crystal meets the parallelism requirements; if it meets the requirements, proceed with the following steps:

[0049] Check and confirm whether the condition of the ring polishing die on the ring polishing machine meets the process requirements before fine repair. If it does not meet the process requirements before fine repair, then repair the ring polishing die until it meets the process requirements.

[0050] Use a goniometer to observe and determine the thin and thick ends of the flat crystal;

[0051] The flat crystal is precision-finished using a ring polishing machine.

[0052] Specifically, such as Figure 1As shown, the process flow in this embodiment is as follows:

[0053] Step S1: Check the surface shape and parallelism of the flat crystal, and take a certain plane of the flat crystal that meets the process requirements before fine finishing as the reference plane; if there is no plane that meets the process requirements before fine finishing, use a ring polisher to polish any plane of the flat crystal until it meets the process requirements before fine finishing and use it as the reference plane.

[0054] Step S2: Check and confirm whether the ring polishing die on the ring polishing machine meets the process requirements before fine repair. If it does not meet the process requirements before fine repair, then repair the ring polishing die until it meets the process requirements.

[0055] Step S3: Use a goniometer to observe and determine the thin and thick ends of the flat crystal;

[0056] Step S4: Use a ring polishing machine to refine the flat crystal.

[0057] Specifically, a protective adhesive is applied to the non-processed surface to protect against defects on the flat crystal surface. In this embodiment, the appropriate protective adhesive is selected according to the flat crystal material. Preferably, the commonly used protective adhesive is acetal adhesive. The cleaning process uses industrial ethanol to wash away the protective adhesive on the flat crystal surface.

[0058] Furthermore, the pre-finishing process requirements for the flat crystal include a surface aperture of ≤0.5, a local aperture of ≤0.2, and a flat crystal parallelism of ≤20″.

[0059] Furthermore, the pre-finishing process requirements corresponding to the ring polishing die refer to the flat surface shape processed by the ring polishing die achieving an aperture ≤ 0.5 and a local aperture ≤ 0.2.

[0060] Specifically, before processing, a plane interferometer, preferably model XQ15-GⅠ, is used to measure the surface shape of the crystal flat. At least one surface aperture N ≤ 0.5 and a local aperture ΔN ≤ 0.2 are used as the reference surface for crystal flat processing. Otherwise, a ring polisher, preferably model CPM1200, is used to make one surface of the crystal flat meet the surface shape index as the reference surface. After selecting the crystal flat reference surface, the parallelism θ of the crystal flat is checked using a goniometer with a measurement accuracy of 2″, preferably model JJC2S. When θ ≤ 20″, it meets the processing requirements.

[0061] Furthermore, the trimming of the ring polishing die includes:

[0062] When the aperture N of the ring polishing surface is greater than 0.5, the position of the ring polishing correction disk is adjusted by moving it.

[0063] When the local aperture ΔN is greater than 0.2, use a hacksaw blade to draw square grooves on the ring polishing die, and at the same time use a scraper to draw "×" marks on each square to make it more refined.

[0064] Specifically, when measuring the surface shape of a flat crystal using a plane interferometer, at least one surface aperture ≤ 0.5 and a local aperture ≤ 0.2 are required. If not, a surface must be reworked using a ring polisher to achieve the required surface shape as a reference surface.

[0065] Ring polishing die dressing method: When the surface aperture is greater than 0.5, the ring polishing die surface shape needs to be dressed by moving the ring polishing correction disc. When the local aperture is greater than 0.2, the ring polishing die surface shape needs to be dressed by using a hacksaw blade to draw square grooves on the ring polishing die, and simultaneously using a scraper to draw "×" marks on each square. When the surface shape of the machined part meets the requirements of aperture ≤ 0.5 and local aperture ≤ 0.2, the ring polishing die dressing is complete.

[0066] Furthermore, the process of using a goniometer to observe and determine the thickness of the flat crystal is as follows:

[0067] Place the flat crystal on a horizontal plane and align the observation surface of the goniometer objective lens with the surface of the flat crystal.

[0068] Rotate the flat crystal around the central axis perpendicular to the surface of the flat crystal, and observe the cross image on the upper and lower surfaces of the flat crystal with a goniometer;

[0069] When the flat crystal is rotated until the vertical lines in the cross image of the upper and lower surfaces coincide in the Y-axis direction, the rotation stops;

[0070] Breathe on the lower surface of the optical flat, and the image of the lower surface of the optical flat will darken. Observe the upper and lower surface images of the optical flat to determine the position of the thin and thick ends.

[0071] Furthermore, when the lower surface image of the flat crystal is located above the upper surface image, the thick end of the flat crystal is at the bottom.

[0072] Specifically, such as Figure 2 As shown, to determine the thickness of the optical flat: Use a goniometer (preferred model JJC2S) to observe the parallelism of the optical flat. Rotate the part by hand; the images of the upper and lower surfaces of the optical flat will rotate accordingly. Align the vertical images of the upper and lower surfaces of the optical flat. At this point, according to the principle of light wave interference, the line connecting the thick and thin ends of the optical flat will coincide with the Y-axis of the goniometer's scale. Use the breath test: breathe on the lower surface of the optical flat. The bright image will be the image of the upper surface of the optical flat, and the dark image will be the image of the lower surface. If the bright image is on top, the thick end is on top; conversely, if the bright image is on the bottom, the thick end is on the bottom.

[0073] Furthermore, the fine finishing of the flat crystal specifically involves placing the flat crystal in a ring polisher with a surface shape that meets the requirements, and fine finishing the processed surface of the flat crystal according to preset parameters.

[0074] Furthermore, the preset parameters include:

[0075] The softening point of the asphalt mold for the ring polisher is 64 degrees Celsius when 60# and 65# asphalt are mixed in a 1:4 ratio.

[0076] Ambient temperature: 22℃~24℃;

[0077] Temperature gradient: <1℃ / h;

[0078] Relative humidity: 30%–70%;

[0079] Equipment rotation speed: 2 r / min ~ 3 r / min;

[0080] Polishing powder concentration: 0.3%–0.5%;

[0081] Polishing powder flow rate: 0.8 L / h ~ 1.0 L / h;

[0082] Powder addition method: Automatic non-recirculating addition of polishing powder;

[0083] Processing time: 2 hours to 3 hours;

[0084] Select an appropriate load to hold down the thick end of the flat crystal during the finishing process.

[0085] Specifically, the main functions of each parameter control in the process parameters are as follows:

[0086] Before processing, check the surface shape of the parts: The surface shape of high-precision flat crystal will affect its parallelism accuracy, so after processing, it is necessary to ensure that the surface shape of the two surfaces reaches a high level, usually requiring an aperture ≤ 0.5 and a local aperture ≤ 0.2;

[0087] Check the parallelism of the flat crystal before processing: The parallelism of the flat crystal before processing determines the processing time of the flat crystal on the ring polisher;

[0088] Environmental temperature and humidity requirements: to ensure the stability of the surface shape of the ring polishing die, which indirectly affects the surface shape and surface defects of the flat crystal;

[0089] Requirements for the surface shape of the polishing mold: During processing, the surface shape of the polishing mold is copied onto the crystal flat. The quality of the polishing mold determines the quality of the surface shape of the crystal flat. Before each processing, the surface shape of the polishing mold must be checked, and the daily changes in the surface shape of the polishing mold should be analyzed based on the results of the previous day's inspection. If it does not meet the requirements, it should be adjusted in time.

[0090] Polishing powder concentration and flow rate: ensure the polishing efficiency and surface defect level of the flat crystal.

[0091] Furthermore, the appropriate load is calculated based on the correspondence between the change in parallelism Δθ of the optical flat and the repair time t and diameter D of the optical flat, and then rounded up, expressed as a formula:

[0092] M=ceil(Δθ·D 2 / (184000·t)), where ceil represents rounding up.

[0093] Furthermore, the parallelism range of the refined flat crystal is 1″ to 2″.

[0094] Specifically, according to preset parameters, a CPM1200 ring polishing machine is preferred, with the following requirements for the polishing die surface: aperture ≤ 0.5, local aperture ≤ 0.2; ambient temperature: 22℃~24℃; the polishing powder is preferably cerium oxide or ferric oxide, with a powder concentration of 0.3%~0.5%; a powder flow rate of 0.8l / h~1.0l / h; a machine speed of 2~3r / min; and a processing time of 2h~3h (depending on part size, parallelism, and load). Figure 3 As shown, the load weight used to press the thick end of the part is: the appropriate load is selected according to the part diameter and the parallelism before fine finishing.

[0095] Place the flat crystal in the running ring of the ring polisher, trim the non-reference surfaces of the flat crystal, and apply a load to the thick end of the flat crystal. Generally, the provided loads are of standard weight. Given a fixed amount of parallelism change and flat crystal diameter, a heavier load results in a shorter processing time. Therefore, the formula is: M = ceil(Δθ·D) 2 The ratio of the required load to the time can be obtained by using / (184000·t). Then, round up. Generally, the heaviest possible weight is selected based on this ratio to shorten the processing time.

[0096] Specifically, in this embodiment, a K9 material flat crystal with a diameter of φ180×15mm is to be finely processed. Before processing, the parallelism θ=20″, the surface shape reaches the aperture N=0.5, and the local aperture ΔN=0.2. After determining its thick end by breathing on it, a protective glue is applied to the non-processed surface. The surface shape of the polishing mold reaches the aperture N≤0.5, and the local aperture ΔN≤0.2. The ambient temperature and humidity meet the requirements. The polishing powder concentration is 0.5%. The polishing powder flow rate is 1.0l / h, and the ring polisher speed is 2.5r / min. The flat crystal is placed on the ring polisher, and a 1.0kg load is placed on the thick end of the flat crystal. After processing for 2 hours, the parallelism of the part becomes 8″. After processing for about 70 minutes, the parallelism of the flat crystal becomes 1″~2″.

[0097] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for precision finishing the parallelism of a large optical flat, comprising: The method includes the following steps: Check the parallelism of the flat crystal. For flat crystals that meet the parallelism requirements, take a certain plane of the flat crystal that meets the process requirements before fine finishing as the reference plane. If there is no plane that meets the process requirements before fine finishing, use a ring polisher to polish any plane of the flat crystal until it meets the process requirements before fine finishing and take it as the reference plane. Based on the reference plane of the flat crystal, check whether the parallelism of the flat crystal meets the parallelism requirements; if it meets the requirements, proceed with the following steps: Check and confirm whether the condition of the ring polishing die on the ring polishing machine meets the process requirements before fine repair. If it does not meet the process requirements before fine repair, then repair the ring polishing die until it meets the process requirements. The process of determining the thickness of the flat crystal using a goniometer is as follows: Place the flat crystal on a horizontal plane and align the observation surface of the goniometer objective lens with the surface of the flat crystal. Rotate the flat crystal around the central axis perpendicular to the surface of the flat crystal, and observe the cross image on the upper and lower surfaces of the flat crystal with a goniometer; When the flat crystal is rotated until the vertical lines in the cross image of the upper and lower surfaces coincide in the Y-axis direction, the rotation stops; Breathe on the lower surface of the optical flat. The image of the lower surface of the optical flat will darken. Observe the upper and lower surface images of the optical flat to determine the position of the thin and thick ends. The flat crystal is precision-finished using a ring polishing machine.

2. The method of claim 1, wherein the method is used for a large optical flat. The pre-finishing process requirements for the flat crystal include a surface aperture of ≤0.5, a local aperture of ≤0.2, and a flat crystal parallelism of ≤20″.

3. The method of claim 2, wherein the method further comprises: The pre-finishing process requirements for the flat crystal also include the pre-finishing process requirements for the ring polishing die, which means that the flat crystal surface processed by the ring polishing die has an aperture ≤ 0.5 and a local aperture ≤ 0.

2.

4. The method of claim 3, wherein the method further comprises: The trimming of the ring polishing die includes: When the aperture of the ring polishing die is greater than 0.5, the position of the ring polishing correction disk is adjusted by moving it. When the local aperture is greater than 0.2, use a hacksaw blade to draw square grooves on the ring polishing die, and at the same time use a scraper to make "×" marks on each square to make it more refined.

5. The method of claim 1, wherein the method is used for large optical flat parallelism finishing. When the lower surface image of the flat crystal is located above the upper surface image, the thick end of the flat crystal is at the bottom.

6. The method of claim 5, wherein the method further comprises: The fine finishing of the flat crystal specifically involves placing the flat crystal in a ring polisher with a surface shape that meets the requirements, and fine finishing the processed surface of the flat crystal according to preset parameters.

7. The method of claim 6, wherein the method further comprises: The preset parameters include The softening point of the asphalt mold for the ring polisher is 64 degrees Celsius when 60# and 65# asphalt are mixed in a 1:4 ratio. Ambient temperature: 22℃~24℃; Temperature gradient: <1℃ / h; Relative humidity: 30%–70%; Equipment rotation speed: 2-3 r / min; Polishing powder concentration: 0.3%~0.5%; Polishing powder flow rate: 0.8~1.0l / h; Processing time: Check every 2-3 hours; Select an appropriate load to hold down the thick end of the flat crystal during the finishing process.

8. The method of claim 7, wherein the method further comprises: The appropriate load is calculated based on the relationship between the change in parallelism Δθ of the optical flat and the repair time t and diameter D of the optical flat, and then rounded up, expressed as a formula: M=ceil(Δθ·D 2 / (184000·t)), where ceil represents rounding up.

9. The method of claim 8, wherein the method further comprises: After refinement, the parallelism range of the flat crystal is 1″ to 2″.

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