Special-shaped optical window low-stress clamp and low-stress clamping method

Abstract

The invention provides a low-stress clamp for a special-shaped optical window and a low-stress clamping method. The clamp comprises a base body, the flexible air bag is arranged on the base body, and the flexible air bag is configured to expand during inflation so as to be conformally attached to the clamping face of the special-shaped optical window, so that uniform clamping pressure is applied to the special-shaped optical window; the air supply system is in fluid connection with the flexible air bag and used for supplying compressed air to the flexible air bag; and the limiting structure is arranged on the base body and is used for positioning the special-shaped optical window. According to the structure, the clamping stress caused by shape errors of a workpiece clamping surface is effectively eliminated, and the inherent defects of a vacuum adsorption method are fundamentally overcome. After being inflated, the flexible air bag can generate self-adaptive deformation and actively fit a clamping surface with an uncertain shape error to realize high conformality and fill all microscopic gaps, so that the shape mismatch of a contact surface is converted into uniform deformation of the air bag instead of forced deformation of a workpiece, and the generated clamping stress is fundamentally eliminated.

Description

Technical Field

[0001] This application relates to the field of optical processing technology, specifically to a low-stress fixture and low-stress clamping method for irregularly shaped optical windows. Background Technology

[0002] Depending on the application scenario, the processing error of the surface shape of optical windows typically needs to be controlled within sub-micron to tens of microns. Large-diameter-to-thickness irregularly shaped optical windows often experience significant clamping deformation during fine grinding or polishing, affecting surface accuracy. To address this issue, patent CN202311178244 discloses a low-stress fixture and clamping method. This method uses vacuum adsorption to replace the traditional dispensing and mounting process, improving surface accuracy stability and production efficiency. However, this method is difficult to meet the processing requirements of ultra-high precision, such as sub-micron level surface accuracy optical windows. The main reason is the unavoidable shape error between the suction cup and the window clamping surface. In production practice, the clamping surface is usually a previously rough-machined surface, with a large and uncertain shape error. Even if the suction cup itself has high flatness, there will still be gaps between it and the clamping surface, making it difficult to achieve high conformality. The stress generated by this shape difference between the vacuum fixture and the workpiece will cause clamping deformation. For ultra-high precision (sub-micron level) optical windows, this clamping deformation introduces significant uncertainty into the fine grinding or polishing process. Summary of the Invention

[0003] In view of the above-mentioned defects or deficiencies in the prior art, this application aims to provide a low-stress fixture and a low-stress clamping method for irregularly shaped optical windows, so as to ensure that the clamping effect of the fixture is not affected by the shape of the workpiece clamping surface.

[0004] In a first aspect, this application proposes a low-stress fixture for irregularly shaped optical windows, used to hold irregularly shaped optical windows during fine grinding or polishing processes, comprising: Matrix; A flexible airbag is disposed on the substrate and is configured to expand when inflated to conformally fit the clamping surface of the irregular optical window, thereby applying a uniform clamping pressure to the irregular optical window. An air supply system, fluidly connected to the flexible airbag, is used to supply compressed gas to the flexible airbag; A limiting structure is provided on the substrate for positioning the irregularly shaped optical window.

[0005] According to the technical solution provided in the embodiments of this application, the gas supply system includes an iron pen, which has a hollow structure and a through hole on its side wall for connecting compressed gas externally; the iron pen is rotatably connected to the base through a bearing; the material of the iron pen is stainless steel or aluminum alloy.

[0006] According to the technical solution provided in the embodiments of this application, it also includes a bushing and an end cap connected to the base through a first connector. The bushing, the end cap, and the bottom frustum of the pen together constitute the axial limiting structure of the bearing.

[0007] According to the technical solution provided in the embodiments of this application, the flexible airbag is made of fluororubber material.

[0008] According to the technical solution provided in the embodiments of this application, the limiting structure includes a collar, the collar having a limiting portion that matches the contour of the irregular optical window, and the gap between the limiting portion and the edge of the irregular optical window is 1mm to 1.5mm.

[0009] According to the technical solution provided in the embodiments of this application, the collar is connected to the base through a second connector, and the collar, the flexible airbag and the base are screwed together.

[0010] According to the technical solution provided in the embodiments of this application, the gas supply system further includes a fluororubber rotary sealing ring disposed between the iron pen and the substrate, for maintaining a seal during relative rotation.

[0011] Secondly, this application proposes a low-stress clamping method, employing the low-stress fixture for irregularly shaped optical windows as described above, comprising the following steps: The fixture is installed on the machine tool swing arm, and the position of the fixture is adjusted so that the gap between the limiting structure at the bottom of the fixture and the polishing disc is controlled to be less than the thickness of the irregular optical window. The irregularly shaped optical window is placed within the limiting structure; Drive the swing arm to bring the lower surface of the irregularly shaped optical window into contact with the polishing disc; Compressed gas is introduced into the flexible airbag to inflate it, thereby achieving dynamic conformal fitting with the clamping surface of the irregular optical window and applying a uniformly distributed normal clamping force perpendicular to the polishing disc to the window.

[0012] According to the technical solution provided in the embodiments of this application, the step of introducing compressed gas into the flexible airbag to inflate the airbag and thereby achieve dynamic conformal fitting with the clamping surface of the irregular optical window includes the following steps: An initial low-pressure gas is introduced into the flexible airbag, causing the airbag to undergo initial deformation and make initial contact with the high point area of ​​the clamping surface to form an initial seal. While maintaining the initial low pressure, the material of the flexible airbag is kept under the initial low pressure for a first preset time, so that the material undergoes creep relaxation and gradually increases the contact area with the clamping surface. The gas pressure inside the flexible airbag is increased stepwise or linearly to a preset target working pressure.

[0013] According to the technical solution provided in the embodiments of this application, dynamic pressure compensation is performed during the grinding and polishing process, including the following steps: Real-time monitoring of the polishing resistance applied to the irregularly shaped optical window or the vibration signal of the fixture; The real-time monitoring value of the polishing resistance or the vibration signal is compared with a preset threshold range; When the real-time monitoring value continuously exceeds the preset threshold range, the gas pressure introduced into the flexible airbag is automatically adjusted to change the normal clamping force, so that the monitoring value of the polishing resistance or the vibration signal returns to the preset threshold range.

[0014] Compared with the prior art, the beneficial effects of this application are as follows: First, it effectively eliminates the clamping stress caused by the shape error of the workpiece clamping surface, fundamentally overcoming the inherent defects of the vacuum adsorption method. After inflation, the flexible airbag can generate adaptive deformation, actively conforming to the clamping surface with uncertain shape errors, achieving "high conformity", filling all micro gaps, thus transforming the shape mismatch of the contact surface into the uniform deformation of the airbag itself, rather than the forced deformation of the workpiece, fundamentally eliminating the clamping stress caused by it.

[0015] Second, it provides a reliable clamping guarantee for the processing of sub-micron level ultra-high precision optical windows. Because the clamping stress is greatly suppressed, the workpiece is stable and the deformation is controllable during the processing, which significantly reduces the uncertainty of the fine grinding or polishing process, making it possible to stably and repeatedly achieve sub-micron level surface accuracy.

[0016] Third, it provides uniformly distributed clamping pressure, avoiding localized stress concentration. As a whole pressure vessel, the airbag has equal internal pressure, which is evenly transmitted to the entire clamping area through flexible contact surfaces. This avoids localized pressure concentration points that may occur with traditional mechanical clamping or vacuum adsorption, further ensuring the surface accuracy of the workpiece.

[0017] Fourth, it possesses excellent versatility and adaptability, making it particularly suitable for irregularly shaped parts. The conformal capability of the flexible airbag makes it naturally adaptable to windows of different shapes (circular, rectangular, irregular) and surface profiles. Combined with the matching limiting structure, it can quickly adapt to various irregularly shaped optical windows, improving the versatility of the fixture and production efficiency. Attached Figure Description

[0018] Figure 1 A cross-sectional schematic diagram of the low-stress fixture for irregularly shaped optical windows provided in an embodiment of this application; Figure 2 This is an exploded structural diagram of the low-stress fixture for irregularly shaped optical windows provided in an embodiment of this application.

[0019] The text labels in the image represent: 1. Iron pen; 2. Bushing; 3. End cap; 4. Bearing; 5. First connecting piece; 6. Fluororubber rotary seal ring; 7. Base; 8. Collar; 9. Irregularly shaped optical window; 10. Flexible airbag; 11. Second connecting piece; 12. Limiting structure; 13. First through hole; 14. First threaded hole; 15. Gas storage cavity; 16. Compressed gas inlet; 17. Compressed gas outlet. Detailed Implementation

[0020] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0021] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0022] Example 1 As mentioned in the background section, and in view of the problems in the prior art, this application proposes a low-stress fixture for irregularly shaped optical windows, used to clamp irregularly shaped optical windows during fine grinding or polishing processes, such as... Figure 1-2 As shown, it includes: Matrix 7; A flexible airbag 10 is disposed on the substrate 7. The flexible airbag 10 is configured to expand when inflated to conformally fit the clamping surface of the irregular optical window 9, thereby applying a uniform clamping pressure to the irregular optical window 9. An air supply system, fluidly connected to the flexible airbag 10, is used to supply compressed gas to the flexible airbag 10; Specifically, the central hole of the substrate 7 and the flexible airbag 10 form a sealed air storage cavity 15, which is connected to the compressed air inlet 16 and the compressed air outlet 17. After compressed air is introduced through the compressed air inlet 16, the flexible airbag 10 expands and fits against the clamping surface of the irregularly shaped optical window 9. The expansion of the flexible airbag 10 provides the necessary pressure for the grinding and polishing process. Furthermore, the flexible airbag 10 is highly conformal to the clamping surface of the irregularly shaped optical window 9, and its shape changes accordingly with the surface shape of the clamping surface. This close-fitting clamping effect makes the grinding and polishing pressure distribution more uniform, avoiding the clamping deformation of traditional fixtures.

[0023] A limiting structure 12 is provided on the substrate 7 and is used to position the irregular optical window 9.

[0024] In a preferred embodiment, the gas supply system includes an iron pen 1, which has a hollow structure and a through hole on its side wall for connecting compressed gas externally; the iron pen 1 is rotatably connected to the base 7 via a bearing 4; the material of the iron pen 1 is stainless steel or aluminum alloy.

[0025] In a preferred embodiment, the system further includes a bushing 2 and an end cap 3 connected to the base 7 via a first connector 5. The bushing 2, the end cap 3, and the bottom frustum of the pen 1 together constitute the axial limiting structure 12 of the bearing 4. The first connector 5 is a bolt.

[0026] In a preferred embodiment, the flexible airbag 10 is made of fluororubber material.

[0027] In a preferred embodiment, the limiting structure 12 includes a collar 8 having a limiting portion that matches the contour of the irregular optical window 9, and the gap between the limiting portion and the edge of the irregular optical window 9 is 1 mm to 1.5 mm.

[0028] In a preferred embodiment, the collar 8 is connected to the base 7 via a second connector 11, and the collar 8, the flexible airbag 10, and the base 7 are screwed together. The second connector 11 is a bolt.

[0029] In a preferred embodiment, the gas supply system further includes a fluororubber rotary sealing ring 6 disposed between the iron pen 1 and the substrate 7, for maintaining a seal during relative rotation.

[0030] Specifically, the base 7 serves as the skeleton and mounting platform of the entire fixture. It is a roughly disc-shaped structural component with a central hole for air supply. The upper part of the base 7 is connected to the pen 1 via a bearing 4, while the lower part is used to mount the airbag and collar 8. Its core function is to support all other components and transmit the movement of the machine tool. Preferably, the base 7 is made of non-metallic materials such as nylon or polytetrafluoroethylene. These materials are lightweight, corrosion-resistant, and have a certain vibration damping effect, which helps maintain stability during high-speed rotation and avoids hard contact and scratches with the optical window. The flexible airbag 10 is a sealed bag made of flexible, elastic material and is fixed below the base 7. Its technical principle is based on Pascal's law and the elastic deformation characteristics of flexible materials. When compressed gas is filled, the internal pressure of the airbag is evenly distributed, driving the bag wall to expand outwards. Due to its flexibility, it can actively adapt to and wrap around all the microscopic undulations and unevennesses of the back of the optical window (i.e., the clamping surface) like a soft hand, thereby achieving conformal fit. Conformal fit means that the contact surface shape of the airbag can dynamically and accurately reproduce the actual shape of the workpiece clamping surface, regardless of whether the surface is an ideal plane or a curved surface with previous machining errors. This fit method transforms the pressure applied to the window clamping surface from a concentrated, uneven force (such as the point support of vacuum adsorption or the line contact of a rigid fixture) into a continuous and uniformly distributed surface pressure. It fundamentally eliminates the clamping stress caused by the mismatch between the fixture and the workpiece shape. For submicron precision machining, such minute stresses are enough to cause uncontrollable surface deformation. This structure ensures that the workpiece is stably clamped in a free state, and the machining allowance is removed uniformly, thus directly and effectively guaranteeing the final surface accuracy. The air supply system is a system that provides a power source for the flexible airbag 10. In implementation, it is not a single component, but a fluid passage composed of the iron pen 1, the central hole of the base 7, and the fluororubber rotary sealing ring 6. The iron pen 1 serves as the air inlet, and its interior is hollow, with through holes in the side walls connecting to the external air source. Compressed gas passes through the iron pen 1, through the central hole of the substrate 7, and finally enters and fills the airbag. The system design ensures that the gas can be stably and controllably delivered to the application area. The limiting structure 12's main function is to precisely position and constrain the optical window in the horizontal plane, preventing it from moving or rotating horizontally during polishing, but at the same time, it does not restrict its uniform compression by the airbag in the vertical direction (clamping force direction). Figure 1As shown, the structure is specifically implemented as a collar 8. The inner contour (i.e., the limiting part) of the collar 8 is machined to match the outer contour of the optical window to be processed. For example, if the window is rectangular, the limiting part of the collar 8 is also a rectangular cavity. A small gap of 1mm-1.5mm is maintained between them, and this gap design is crucial: if it is too small, it may jam due to workpiece dimensional tolerances or generate assembly stress; if it is too large, it cannot effectively limit horizontal displacement. This structure ensures that the workpiece can be placed quickly and accurately at the predetermined station and aligned with the projection area of ​​the airbag.

[0031] Specifically, the collar 8 has a first through hole 13, and the base 7 has a first threaded hole 14. The first through hole 13 and the first threaded hole 14 are used to install the second connector 11.

[0032] Specifically, the stator 1 is a slender cylindrical component. Its upper end connects to the machine tool swing arm via a standard interface, thereby suspending the entire fixture. Its hollow structure and sidewall through-holes are the specific structural features for achieving air supply. An external compressed air pipe connector is connected to this sidewall through-hole, allowing gas to flow into the hollow pipe inside the stator 1, forming the first section of the air path. The stator 1 is not only an air transmission component but also the main load-bearing component between the fixture and the machine tool, requiring sufficient strength and rigidity; therefore, its material is preferably stainless steel or aluminum alloy. Stainless steel is corrosion-resistant and has a long service life; aluminum alloy is lightweight, reducing inertial forces during high-speed movement. The stator 1 is connected to the base 7 via a deep groove ball bearing 4. Its technical principle lies in decomposing the fixture's motion into two parts: a stator and a rotor. The stator consists of the stator 1, bushing 2, and the inner ring of the bearing 4. This part is driven by the machine tool swing arm, primarily performing translational motion (e.g., reciprocating motion caused by a crank-connecting rod mechanism). The rotor section consists of the outer ring of bearing 4, the base 7, the collar 8, and the clamped optical window. During the polishing process, a large frictional force is generated between the workpiece and the rotating polishing disc. This frictional force drives the entire rotor section to rotate freely relative to the stator section. The technical effect is to avoid the transfer of additional torsional stress to the optical window due to the clamping mechanism being "stuck," ensuring that the workpiece naturally follows the rotation of the polishing disc during processing, thereby achieving uniform material removal and further reducing the risk of surface shape errors caused by motion interference.

[0033] Specifically, the composition and assembly of the limiting structure 12: This structure is composed of three parts working together: bushing 2, end cap 3, and a frustum at the bottom of the pen 1. Bushing 2: Fitted onto the pen 1, located above or below the inner ring of the bearing 4, used to precisely determine the axial position of the inner ring of the bearing 4 on the shaft of the pen 1. Frustum at the bottom of the pen 1: The pen 1 has a radially protruding frustum structure machined thereon, serving as an axial support surface on the other side of the inner ring of the bearing 4. End cap 3: Fastened to the base 7 by bolts, its inner edge pressing against the outer ring of the bearing 4.

[0034] Implementation Method: During assembly, first, place the bearing 4 onto the stator 1, with one side of its inner ring abutting against the bottom frustum of the stator 1. Then, insert the bushing 2, pressing it against the other side of the inner ring of the bearing 4. Next, place this assembly into the bearing 4 seat of the base 7, so that one side of the outer ring of the bearing 4 contacts the shoulder of the bearing 4 seat. Finally, cover it with the end cap 3 and lock the end cap 3 onto the base 7 with bolts. At this point, the inner side of the end cap 3 precisely presses against the other side of the outer ring of the bearing 4. By pressing the inner and outer rings of the bearing 4 from both above and below (or front and back) directions respectively through these three parts, the axial clearance of the bearing 4 is completely eliminated. This ensures that the rotor part (base 7, etc.) has no axial movement relative to the stator part (stator 1), and can only rotate freely in the circumferential direction. The technical effect is to ensure the dynamic accuracy and rigidity of the fixture under high-speed rotation and translational combined motion. If axial movement exists, it will cause fluctuations in the processing pressure of the optical window, directly affecting the surface accuracy. The bushing 2 is preferably made of aluminum alloy, which is easy to process and lightweight; the end cap 3 is connected to the base 7 by bolts, which ensures structural stability and the convenience of disassembly and maintenance.

[0035] Example 2 Based on Example 1, this example proposes a low-stress clamping method, using the low-stress fixture for the irregularly shaped optical window 9 as described above, including the following steps: The fixture is installed on the machine tool swing arm, and the position of the fixture is adjusted so that the gap between the limiting structure 12 at the bottom of the fixture and the polishing disc is controlled to be less than the thickness of the irregular optical window 9. The irregularly shaped optical window 9 is placed within the limiting structure 12; Drive the swing arm to bring the lower surface of the irregular optical window 9 into contact with the polishing disc; Compressed gas is introduced into the flexible airbag 10 to inflate the airbag, thereby achieving dynamic conformal fitting with the clamping surface of the irregular optical window 9, and applying a uniformly distributed normal clamping force perpendicular to the polishing disc to the window.

[0036] Specifically, the operator first installs and locks the fixture onto the chuck of the machine tool's swing arm via the upper interface of the stylus 1. Then, the operator manually or via the CNC system operates the machine tool, driving the swing arm to move so that the collar 8 at the bottom of the fixture approaches the polishing disc. Using a feeler gauge or the machine tool's tool setter, the operator precisely measures and adjusts the gap H between the lower plane of the collar 8 and the upper surface of the rotating polishing disc. This gap H must be strictly controlled to be less than the thickness T of the optical window to be processed. A preferred embodiment is to control it to 40% to 60% of the window thickness T. For example, for a window with a thickness T = 10 mm, the gap H should be adjusted to 4 mm to 6 mm. With the machine tool swing arm raised, the operator manually or via the automated feeding mechanism carefully places the irregularly shaped optical window 9 into the limiting part of the collar 8. Because the contour of the limiting part matches the shape of the window and leaves a gap of 1 mm to 1.5 mm, the window can be easily and without interference placed in place, and its approximate position and angle are automatically corrected. Using the machine tool's control panel or program, activate the pneumatic or servo drive to control the swing arm to descend smoothly. When it descends to the preset gap position in step one, the lower surface (the surface to be processed) of the optical window 9 will first contact the rotating polishing disc. At this time, the window is supported by the polishing disc, and its own weight is borne by the polishing disc. The operator opens the precision pressure regulating valve connected to the external air source to introduce compressed air into the system. The gas flows through the hollow channel of the iron pen 1, through the central hole of the substrate 7, and enters and fills the flexible airbag 10. The airbag begins to expand under the action of internal pressure, and its soft bottom surface gradually comes into complete contact with the back (clamping surface) of the optical window. By adjusting the pressure regulating valve, the pressure inside the airbag is stabilized at a preset target value (e.g., 0.1 MPa). At this time, a uniform vertical normal clamping force P is applied to the window, pressing it stably against the polishing disc.

[0037] In a preferred embodiment, the step of introducing compressed gas into the flexible airbag 10 to inflate the airbag and achieve dynamic conformal fitting with the clamping surface of the irregularly shaped optical window 9 includes the following steps: An initial low-pressure gas is introduced into the flexible airbag 10, causing the airbag to undergo initial deformation and make initial contact with the high point area of ​​the clamping surface to form an initial seal. While maintaining the initial low pressure, the material of the flexible airbag 10 is kept under the action of the initial low pressure for a first preset time, so that the material undergoes creep relaxation and gradually expands the contact area with the clamping surface. The gas pressure inside the flexible airbag 10 is increased stepwise or linearly to a preset target working pressure.

[0038] Specifically, the operator first sets the precision pressure regulating valve to a low pressure value, such as 0.02 MPa, and then opens the air circuit. This low-pressure gas causes the air bladder to expand slightly, with its most prominent part initially contacting the highest area on the workpiece clamping surface. This gentle contact is sufficient to form an initial, localized seal. A "soft-then-hard" strategy is employed. The initial low pressure avoids the risk of minute workpiece displacement or instantaneous stress caused by the sudden impact of high-pressure gas. Prioritizing contact with the highest point and forming an initial seal establishes a stable foundation for the subsequent expansion of the air bladder. This achieves a smooth start to the clamping process, creating conditions for subsequent fully conformal fitting and avoiding the uncertainties caused by "impact."

[0039] Specifically, after introducing an initial low pressure, this pressure state is maintained for a first preset duration Δt (e.g., 5-15 seconds). During this period, due to the viscoelasticity of flexible materials such as fluororubber, minute, time-dependent deformation occurs under continuous pressure, known as "creep relaxation." This allows the airbag material to fill deeper into the microscopic valleys of the workpiece clamping surface, like a slowly flowing fluid, thereby achieving a gradual and active expansion of the contact area. Active, adaptive conformal fitting is achieved by utilizing the creep behavior of the material. This is a physical relaxation process; it is not forced deformation driven by external power, but rather a slow adjustment of the material's internal structure, achieving stress-free, ultimate fit. This step is crucial for achieving ultra-high precision clamping in this method. It ensures that the airbag and workpiece do not merely "touch," but achieve the maximum possible actual contact area. This directly leads to a highly uniform clamping pressure distribution, which is essential for controlling sub-micron surface shape errors.

[0040] Specifically, after a pressure-holding relaxation period of Δt, the precision pressure regulating valve is slowly adjusted. The pressure inside the airbag can be gradually increased from the initial low pressure to the final target working pressure (e.g., 0.1 MPa) in a stepwise manner (e.g., increasing by 0.02 MPa each time, stabilizing for 2-3 seconds) or in a smooth linear manner. This ultimately establishes a stable, uniform, and controllable normal clamping force on the workpiece. This force ensures that the workpiece does not slip during processing, and its uniformity prevents the introduction of localized stresses that could lead to deformation.

[0041] In a preferred embodiment, dynamic pressure compensation is performed during the grinding and polishing process, including the following steps: Real-time monitoring of the polishing resistance applied to the irregular optical window 9 or the vibration signal of the fixture; The real-time monitoring value of the polishing resistance or the vibration signal is compared with a preset threshold range; When the real-time monitoring value continuously exceeds the preset threshold range, the gas pressure introduced into the flexible airbag 10 is automatically adjusted to change the normal clamping force, so that the monitoring value of the polishing resistance or the vibration signal returns to the preset threshold range.

[0042] Specifically, a monitoring system is activated after the grinding and polishing process begins. Implementation Method 1: A force sensor is installed on the machine tool spindle or swing arm to monitor the drive motor current in real time or directly measure the grinding and polishing resistance (tangential force) applied to the workpiece. Implementation Method 2: A vibration acceleration sensor is installed on the fixture base 7 or the machine tool to monitor vibration signals during the processing in real time. Data from these sensors is collected in real time and transmitted to a PLC (Programmable Logic Controller) or industrial PC. In the control system, based on process experiments and experience, a stable range for the grinding and polishing resistance (e.g., 50N-70N) or an effective range for vibration acceleration (e.g., less than 0.5 m / s²) is preset. The control system continuously compares the real-time collected monitoring values ​​with this preset threshold range. When the control system detects that the monitored signal (e.g., grinding and polishing resistance) is continuously (e.g., for more than 2 seconds) above the upper limit, it determines that the normal clamping force may be too large, leading to increased frictional resistance. The system automatically outputs a control signal to the electro-proportional valve (as an upgrade to the precision pressure regulating valve), slightly reducing (e.g., lowering by 0.01 MPa) the pressure inside the air chamber. Conversely, if the signal remains below the lower limit, the air chamber pressure is slightly increased. Through such a closed-loop negative feedback control system, the clamping force is dynamically adjusted to keep the processing state stable within the ideal threshold range.

[0043] This implementation method ensures that low stress and high stability are not only achieved at the moment of clamping, but are maintained continuously throughout the entire processing cycle. This effectively combats uncertainties in the processing, significantly improves the consistency of surface accuracy and yield, and is the ultimate guarantee for achieving stable, mass production of sub-micron level ultra-high precision optical windows.

[0044] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. The above descriptions are only preferred embodiments of this application. It should be noted that due to the limitations of written expression, while there are objectively infinite specific structures, those skilled in the art can make several improvements, modifications, or changes without departing from the principles of this invention, and can also combine the above technical features in an appropriate manner. These improvements, modifications, changes, or combinations, or the direct application of the inventive concept and technical solution to other situations without modification, should all be considered within the scope of protection of this application.

Claims

1. A low-stress fixture for irregularly shaped optical windows, used for clamping irregularly shaped optical windows (9) during fine grinding or polishing, characterized in that, include: Matrix (7); A flexible airbag (10) is disposed on the substrate (7). The flexible airbag (10) is configured to expand when inflated to conformally fit the clamping surface of the irregular optical window (9), thereby applying a uniform clamping pressure to the irregular optical window (9). An air supply system, fluidly connected to the flexible airbag (10), is used to supply compressed gas to the flexible airbag (10); A limiting structure (12) is provided on the substrate (7) for positioning the irregular optical window (9).

2. The low-stress fixture for irregularly shaped optical windows according to claim 1, characterized in that: The gas supply system includes an iron pen (1), which has a hollow structure and a through hole on its side wall for connecting to compressed gas. The iron pen (1) is rotatably connected to the base (7) through a bearing (4). The material of the iron pen (1) is stainless steel or aluminum alloy.

3. The low-stress fixture for irregularly shaped optical windows according to claim 2, characterized in that: It also includes a bushing (2) and an end cap (3) connected to the base (7) via a first connector (5). The bushing (2), the end cap (3) and the bottom frustum of the pen (1) together constitute the axial limiting structure (12) of the bearing (4).

4. The low-stress fixture for irregularly shaped optical windows according to claim 1, characterized in that: The flexible airbag (10) is made of fluororubber material.

5. The low-stress fixture for irregularly shaped optical windows according to claim 1, characterized in that: The limiting structure (12) includes a collar (8) having a limiting portion that matches the contour of the irregular optical window (9), and the gap between the limiting portion and the edge of the irregular optical window (9) is 1 mm to 1.5 mm.

6. The low-stress fixture for irregularly shaped optical windows according to claim 5, characterized in that: The collar (8) is connected to the base (7) via the second connector (11), and the collar (8), the flexible airbag (10) and the base (7) are screwed together.

7. The low-stress fixture for irregularly shaped optical windows according to claim 1, characterized in that: The gas supply system also includes a fluororubber rotary sealing ring (6) disposed between the iron pen (1) and the substrate (7) to maintain a seal during relative rotation.

8. A low-stress clamping method, employing a low-stress clamp for irregularly shaped optical windows as described in any one of claims 1 to 7, characterized in that: Includes the following steps: The fixture is installed on the machine tool swing arm, and the position of the fixture is adjusted so that the gap between the limiting structure (12) at the bottom of the fixture and the polishing disc is controlled to be less than the thickness of the irregular optical window (9). The irregularly shaped optical window (9) is placed inside the limiting structure (12); Drive the swing arm so that the lower surface of the irregular optical window (9) contacts the polishing disc; Compressed gas is introduced into the flexible airbag (10) to inflate the airbag, thereby achieving dynamic conformal fitting with the clamping surface of the irregular optical window (9) and applying a uniformly distributed normal clamping force perpendicular to the polishing disc to the window.

9. The low-stress clamping method according to claim 8, characterized in that: The process of introducing compressed gas into the flexible airbag (10) to inflate the airbag and achieve dynamic conformal fitting with the clamping surface of the irregular optical window (9) includes the following steps: An initial low-pressure gas is introduced into the flexible airbag (10) to cause the airbag to undergo initial deformation and make initial contact with the high point area of ​​the clamping surface to form an initial seal. While maintaining the initial low pressure, the material of the flexible airbag (10) is kept under the action of the initial low pressure for a first preset time, so that the material undergoes creep relaxation and gradually expands the contact area with the clamping surface. The gas pressure inside the flexible airbag (10) is increased stepwise or linearly to a preset target working pressure.

10. The low-stress clamping method according to claim 8, characterized in that: During the grinding and polishing process, dynamic pressure compensation is performed, including the following steps: Real-time monitoring of the polishing resistance applied to the irregular optical window (9) or the vibration signal of the fixture; The real-time monitoring value of the polishing resistance or the vibration signal is compared with a preset threshold range; When the real-time monitoring value continues to exceed the preset threshold range, the gas pressure introduced into the flexible airbag (10) is automatically adjusted to change the normal clamping force, so that the monitoring value of the polishing resistance or the vibration signal returns to the preset threshold range.

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