Low-vibration optical device for vacuum environments and design method

Abstract

The present application belongs to the technical field of precise optical experimental device, and particularly relates to a low-vibration optical device suitable for vacuum environment and a design method. In view of the problem that the structural rigidity and vibration transmission performance of a large-size optical device in a vacuum environment are difficult to be considered, the present application comprises a threaded hole array for mounting and fixing optical elements on the surface of an optical plate, a frame structure fixedly connected to the bottom surface of the optical plate, the frame structure being a support grid framework made of vacuum-compatible metal material, and a plurality of counterweights and supporting legs arranged at the bottom of the frame structure. By inputting ground vibration excitation and loading additional mass, vibration response of the top of the device is obtained, quantitative evaluation of the vibration transmission characteristics is realized, and the counterweights and the frame structure are iteratively optimized based on the evaluation results, so that a design scheme meeting the indicators is finally determined.

Description

Technical Field

[0001] This invention belongs to the technical field of precision optical experimental devices, specifically relating to a low-vibration optical device and design method suitable for vacuum environments, which can be applied to gravitational wave detection, precision laser interferometry, quantum precision measurement and other ultra-high vacuum optical experimental systems. Background Technology

[0002] In the fields of precision optical experiments and high-sensitivity measurements, such as gravitational wave detection, laser interferometry, and quantum precision measurement, extremely high requirements are placed on the stability of optical systems. Even extremely small relative displacements between optical components can cause changes in the optical path length, leading to interference signal drift or even measurement errors. Therefore, the platform structure supporting the optical components is required to have high stability and low vibration characteristics.

[0003] In practical engineering environments, ground vibration is one of the main external disturbances affecting the stability of optical systems. Ground vibration typically originates from natural geological activities, human activities, and mechanical disturbances caused by the operation of buildings or equipment. Its frequency range is wide, but it is particularly significant in the low-frequency band. This type of vibration is transmitted to the optical platform through the foundation structure, causing the platform to produce minute translational and rotational responses, which in turn affects the spatial positional stability of optical components and reduces the system's measurement accuracy.

[0004] To reduce the impact of ground vibrations on optical systems, vibration isolation structures or supports are typically used in engineering to attenuate vibrations, such as passive or active vibration control, to reduce the influence of external vibration inputs on the system. However, in the low-frequency range, the vibration isolation effect may be limited due to the inherent frequency and dynamic constraints of the isolation system, and vibration amplification may even occur in certain frequency ranges, especially in vacuum environments or high-precision optical experimental conditions, where this problem is more prominent.

[0005] Furthermore, existing technologies for analyzing the vibration performance of optical platforms typically employ modal analysis or deterministic analysis methods based on simplified loads. These methods fail to adequately consider the stochastic characteristics of real ground vibrations and accurately reflect the structure's response propagation behavior in the frequency domain. Simultaneously, there is a lack of quantitative evaluation methods based on actual ground vibration spectrum data for comparing the vibration transmission performance of different structural design schemes. This makes the structural optimization process rely to some extent on empirical judgment and lacks a unified engineering analysis basis.

[0006] Therefore, how to establish a finite element analysis model of an optical platform considering the boundary conditions of a vacuum environment and the random vibration input of the real ground, and how to solve the vibration response and quantitatively evaluate the transmission characteristics based on the amplitude spectral density input, has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] To address the challenge of balancing structural rigidity and vibration transmission performance in large-size optical devices operating in a vacuum environment, this invention provides a low-vibration optical device and design method suitable for vacuum environments.

[0008] To achieve the above objectives, the present invention employs the following technical solution:

[0009] The present invention provides a low-vibration optical device suitable for vacuum environments, including an optical plate. The surface of the optical plate is provided with an array of threaded holes for mounting and fixing optical elements. A frame structure is fixedly connected to the bottom surface of the optical plate. The frame structure is a support grid skeleton made of vacuum-compatible metal material. Multiple counterweights and legs are provided at the bottom of the frame structure.

[0010] Furthermore, the frame structure is provided with orthogonal main ribs and diagonal reinforcing ribs arranged at a 45° angle to the orthogonal main ribs. The orthogonal main ribs and diagonal reinforcing ribs together form a composite mesh topology skeleton. The composite mesh topology skeleton includes multiple square mesh units. Each square mesh unit is further divided into triangular high-stiffness support units by diagonal reinforcing ribs.

[0011] Furthermore, the optical plate and the frame structure are welded to form an integrated box structure, and the overall shape of the integrated box structure is a regular octagon; the threaded hole array is evenly distributed on the surface of the optical plate, including threaded segments set on the upper surface of the optical plate and venting holes communicating with the threaded segments, and the venting holes penetrate the optical plate.

[0012] Furthermore, the counterweight has a concave structure that is narrow at the top and wide at the bottom. Multiple counterweights are disposed in the bottom peripheral area of ​​the frame structure and are arranged symmetrically about the geometric center of the optical device. The counterweights are detachably connected to the frame structure by vacuum-compatible fasteners to lower the overall center of gravity of the optical device and suppress rigid body pitch and roll mode vibrations.

[0013] Furthermore, the support leg includes an upper support section, a middle cylindrical connecting section, and a bottom flange connecting section; the top surface of the upper support section contacts the bottom surface of the frame structure and provides support; the bottom flange connecting section is fixedly connected to the vacuum chamber floor plate by a vacuum-compatible fastener; the vacuum-compatible fastener has an exhaust channel running through it along the axial direction.

[0014] This invention also provides a design method for a low-vibration optical device suitable for vacuum environments, comprising the following steps:

[0015] Step 1, establish a three-dimensional finite element solid model: according to the preset geometric configuration parameters, construct a three-dimensional finite element solid model including optical plate, frame structure, counterweight and legs, and assign corresponding elastic modulus, Poisson's ratio, density and isotropic loss factor according to the actual material properties.

[0016] Step 2, establish ground constraint boundary conditions: apply a rigid connector to the bottom of the outrigger, constrain the rotational degrees of freedom of the rigid connector about the X-axis, Y-axis and Z-axis, and apply additional mass and corresponding moment of inertia to the rigid connector to construct an equivalent large mass base, thereby realizing the equivalent simulation of the ground rigid boundary conditions through the inertial effect;

[0017] Step 3, Modal characteristic analysis: Perform characteristic frequency analysis on the three-dimensional finite element solid model to obtain the natural frequencies and corresponding mode shapes of the optical device, and determine the main vibration mode characteristics of the optical device;

[0018] Step 4, Constructing a ground vibration excitation model: Based on the frequency domain dynamic relationship, the measured ground vibration displacement amplitude spectral density is calculated. The equivalent power spectral density is converted into the equivalent power spectral density acting on the ground equivalent boundary conditions. This equivalent power spectral density is then applied to the ground equivalent boundary conditions to establish a stochastic vibration analysis model. The expression is:

[0019] ;

[0020] Where m is the equivalent mass corresponding to the ground equivalent boundary conditions. It is frequency;

[0021] Step 5, Solve for random vibration response: Based on the modal characteristic analysis results, solve the frequency domain response of the random vibration analysis model to obtain the vibration response of the optical device under ground vibration excitation.

[0022] Step 6, extract and evaluate vibration transmission characteristics: extract the vibration response amplitude spectral density at the target measurement position of the optical plate, and compare and analyze it with the input ground vibration displacement amplitude spectral density to obtain the vibration transmission characteristics of the optical device;

[0023] Step 7, Parameter Optimization and Design Scheme Determination: Determine whether the vibration transmission characteristics meet the preset low vibration index requirements; if they do, then determine the current geometric configuration parameters as the final design scheme; if they do not, then modify the shape, mass and installation position of the counterweight, or the shape and width of the frame structure, and return to Step 1 to remodel and calculate until the index is met, thus completing the design of the optical device.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] Existing large-size optical platforms typically employ solid plates, stiffening rib structures, or honeycomb sandwich structures to enhance rigidity. However, while meeting high rigidity requirements, these methods often suffer from issues such as significant structural mass, complex vibration transmission paths, and difficulties in gas release under vacuum conditions. This invention utilizes an integrated design of the optical plate and frame structure. An open grid skeleton composed of orthogonal main ribs and diagonal stiffeners improves structural rigidity and characteristic frequencies, while simultaneously reducing enclosed space and enhancing applicability in vacuum environments.

[0026] Furthermore, by setting counterweights to optimize the mass distribution of the device, this invention lowers the overall center of gravity of the optical device and suppresses rigid body pitch and roll mode vibrations, thereby improving the stability of the optical working surface.

[0027] During the device design process, the vibration response at the top of the device is obtained by inputting actual ground vibration excitation and loading additional mass, thereby achieving a quantitative assessment of the vibration transmission characteristics. Based on the assessment results, the counterweight and frame structure are iteratively optimized to finally determine a design scheme that meets the vibration index requirements.

[0028] Therefore, while meeting the requirements of ultra-high vacuum compatibility, this invention improves the structural characteristic frequency and reduces the transmission of ground vibration to the optical working surface, and can be applied to ground-based gravitational wave detection and precision optical measurement systems. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the overall structure of the low-vibration optical device of the present invention;

[0030] Figure 2 This is a schematic diagram of the frame structure;

[0031] Figure 3 The curves show the comparison between the vertical vibration displacement amplitude spectral density (ASD) at the measurement position at the center of the top surface of the optical plate and the ground input displacement amplitude spectral density (ASD).

[0032] Figure 4 The curves show the comparison between the amplitude spectral density (ASD) of the horizontal vibration displacement at the measurement position at the center of the top surface of the optical plate and the amplitude spectral density (ASD) of the ground input displacement. Detailed Implementation

[0033] To further illustrate the technical solution of the present invention, the present invention will be further described below through embodiments.

[0034] Example 1

[0035] like Figure 1As shown, a low-vibration optical device suitable for vacuum environment in this embodiment includes an optical plate 1. The surface of the optical plate 1 is provided with an array of threaded holes for mounting and fixing optical elements. A frame structure 2 is fixedly connected to the bottom surface of the optical plate 1. The frame structure 2 is a support grid skeleton made of vacuum compatible metal material. Multiple counterweights 3 and support legs 4 are provided at the bottom of the frame structure 2.

[0036] The optical plate 1 and the frame structure 2 are welded together to form an integrated box structure. The overall shape of the integrated box structure is a regular octagon. The threaded hole array is evenly distributed on the surface of the optical plate 1, including a threaded segment on the upper surface of the optical plate 1 and an exhaust hole communicating with the threaded segment. The exhaust hole penetrates the optical plate 1.

[0037] like Figure 2 As shown, the frame structure 2 is equipped with orthogonal main reinforcement bars and diagonal reinforcement bars arranged at a 45° angle to the orthogonal main reinforcement bars. The orthogonal main reinforcement bars and diagonal reinforcement bars together form a composite grid topology skeleton. The composite grid topology skeleton includes multiple square grid units. Each square grid unit is further divided into triangular high-rigidity support units by diagonal reinforcement bars, which effectively reduces the structural mass while ensuring structural rigidity.

[0038] The counterweight 3 has a concave structure that is narrow at the top and wide at the bottom. Multiple counterweights 3 are set in the bottom outer area of ​​the frame structure 2 and are arranged symmetrically about the geometric center of the optical device. The counterweights 3 are detachably connected to the frame structure 2 by vacuum-compatible fasteners to lower the overall center of gravity of the optical device and suppress rigid body pitch and roll mode vibrations.

[0039] The support leg 4 includes an upper support section, a middle cylindrical connecting section, and a bottom flange connecting section; the top surface of the upper support section contacts the bottom surface of the frame structure 2 and provides support; the bottom flange connecting section is fixedly connected to the vacuum chamber floor plate by vacuum-compatible fasteners.

[0040] In this embodiment, the optical device adopts an overall octagonal structure with a side-to-side distance of 2640 mm and a total height of 80 mm. The optical plate 1 and the frame structure 2 are made of vacuum-compatible metal material, preferably 316 stainless steel, with a thickness of 40 mm. The two are fixedly connected by welding to form an integrated double-layer box-shaped composite platform structure, thereby improving the overall bending stiffness and modal frequency of the device.

[0041] The optical plate 1 is a solid plate structure with threaded mounting holes evenly distributed in a 25 mm × 25 mm array on its upper surface for mounting and positioning optical components, lens mounts, and experimental devices. To meet the requirements of precision optical experiments, the overall flatness of the working surface of the optical plate 1 is better than 0.5 mm, and the flatness of the central 600 mm × 600 mm working area used for mounting key optical components is better than 0.1 mm.

[0042] The diameter of the cylindrical connecting section in the middle of the outrigger 4 is 150 mm, and the center distance between the outriggers is 2300 mm. The thickness of the disc of the bottom flange connecting section is 37 mm, and it is fixedly connected to the vacuum chamber floor plate through the mounting through hole and vacuum-compatible fasteners to form a stable and reliable support boundary.

[0043] To optimize the overall dynamic characteristics of the device, multiple counterweights 3 are arranged in the bottom peripheral area of ​​the frame structure 2, preferably four in this embodiment. The counterweights 3 are arranged symmetrically about the geometric center of the device and are detachably connected to the frame structure 2 by vacuum-compatible fasteners. The counterweights 3 have a concave structure, with the upper width being smaller than the lower width, so that more mass is distributed in the lower region of the device.

[0044] By rationally configuring the mass and installation position of the counterweight 3, the overall center of gravity of the device can be lowered to the bottom area of ​​the frame structure 2, and the overall center of gravity position can be made close to the support plane. This significantly reduces the tilt coupling effect in the pitch and roll directions of the device, improves the stability of the device to low-frequency vibration disturbances, and improves the overall vibration transmission performance.

[0045] The vacuum-compatible fasteners used have an axially through-venting channel inside. This venting channel runs through the fastener along its axis, which can avoid the formation of local closed air cavities, reduce gas retention in the vacuum environment, improve pumping efficiency, and reduce the impact of the gas spring effect on the structural vibration performance.

[0046] This embodiment also provides a design method for the above-mentioned optical device, which specifically includes the following steps:

[0047] Step 1, establish a three-dimensional finite element solid model: according to the preset geometric configuration parameters, construct a three-dimensional finite element solid model including optical plate 1, frame structure 2, counterweight block 3 and support leg 4, and assign corresponding elastic modulus, Poisson's ratio, density and isotropic loss factor according to the actual material properties.

[0048] Step 2, establish ground constraint boundary conditions: apply a rigid connector to the bottom of the outrigger 4, constrain the rotational degrees of freedom of the rigid connector about the X-axis, Y-axis and Z-axis, and apply additional mass and corresponding moment of inertia to the rigid connector to construct an equivalent large mass base, and realize the equivalent simulation of the ground rigid boundary conditions through the inertial effect;

[0049] Step 3, Modal characteristic analysis: Perform characteristic frequency analysis on the three-dimensional finite element solid model to obtain the natural frequencies and corresponding mode shapes of the optical device, and determine the main vibration mode characteristics of the optical device;

[0050] Step 4, Constructing a ground vibration excitation model: Based on the frequency domain dynamic relationship, the measured ground vibration displacement amplitude spectral density is calculated. The equivalent power spectral density is converted into the equivalent power spectral density acting on the ground equivalent boundary conditions. This equivalent power spectral density is then applied to the ground equivalent boundary conditions to establish a stochastic vibration analysis model. The expression is:

[0051] ;

[0052] Where m is the equivalent mass corresponding to the ground equivalent boundary conditions. It is frequency;

[0053] Step 5, Solve for random vibration response: Based on the modal characteristic analysis results, solve the frequency domain response of the random vibration analysis model to obtain the vibration response of the optical device under ground vibration excitation.

[0054] Step 6, extract and evaluate vibration transmission characteristics: extract the vibration response amplitude spectral density at the target measurement position of optical plate 1, and compare and analyze it with the input ground vibration displacement amplitude spectral density to obtain the vibration transmission characteristics of the optical device;

[0055] Step 7, Parameter Optimization and Design Scheme Determination: Determine whether the vibration transmission characteristics meet the preset low vibration index requirements; if they do, then determine the current geometric configuration parameters as the final design scheme; if they do not, then modify the shape, mass and installation position of the counterweight 3, or the shape and width of the frame structure 2, and return to Step 1 to remodel and calculate until the index is met, thus completing the design of the optical device.

[0056] Dynamic simulation was performed using the design method of this embodiment, and the calculation results are as follows: Figure 3 and Figure 4 As shown. Figure 3 and Figure 4 The figures show comparison curves of the amplitude spectral density (ASD) of vibration displacement in the vertical and horizontal directions at the measurement position at the center of the top surface of optical plate 1, and the ASD of the ground input displacement displacement. In the figures, the horizontal axis represents frequency (Hz), ranging from 0.01 Hz to 1000 Hz; the vertical axis represents displacement amplitude spectral density, in m / sqrt(Hz). The green curve representing "ground" indicates the input random vibration spectrum of the ground, and the red curve representing "device" indicates the response spectrum of the target area on the top surface of optical plate 1.

[0057] Depend on Figure 3 The corresponding vertical dynamic response spectrum shows that in the extremely low frequency range of 0.01 Hz to 10 Hz, the response spectrum (red) of the device exhibits a very high degree of overlap and rigid tracking characteristics with the ground input spectrum (green). Analysis results indicate that this invention successfully achieves the physical lowering of the overall center of gravity of the device by symmetrically arranging concave counterweights 3 (narrower at the top and wider at the bottom) around the bottom periphery of the frame structure 2, bringing it closer to the supporting plane. This reduces the tilt coupling effect of rigid body pitch and roll modes caused by ultra-low frequency ground disturbances and lowers the common resonance amplification phenomenon in the low-frequency range. In the frequency range of 10 Hz to 1000 Hz, although local resonance peaks appear due to the influence of the inherent elastic modes of the structure, the optical plate 1 and frame structure 2 are welded together to form an integrated double-layer box structure. Furthermore, the internal high-stiffness triangular composite mesh topology skeleton, composed of orthogonal main ribs and 45° oblique reinforcing ribs, greatly improves the overall bending stiffness of the device, raising the first-order characteristic frequency and effectively avoiding the dense low-frequency noise area on the ground.

[0058] Depend on Figure 4 The corresponding horizontal dynamic response spectrum shows that the device achieves rigid tracking of ground vibrations without amplification in the low-frequency range of 0.01 Hz to 10 Hz. However, in the mid-to-high frequency range (especially above 30 Hz), the device's response spectrum is generally lower than the ground input spectrum, exhibiting a good vibration transmission suppression effect in multiple frequency bands.

[0059] In summary, Figure 3 and Figure 4 The analysis results show that the low-vibration optical device optimized using the design method described in this invention can balance large structural size, ultra-high structural stiffness, and good vibration transmission suppression performance in an ultra-high vacuum environment. It is suitable for the stringent engineering requirements of dynamic stability in ground-based gravitational wave detection systems, high-sensitivity laser interferometry, and precision optical measurement systems.

[0060] The foregoing has shown and described the main features and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0061] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A low-vibration optical device suitable for vacuum environments, characterized in that, The optical plate (1) has an array of threaded holes on its surface for mounting and fixing optical elements. A frame structure (2) is fixedly connected to the bottom surface of the optical plate (1). The frame structure (2) is a support grid skeleton made of vacuum-compatible metal material. Multiple counterweights (3) and legs (4) are provided at the bottom of the frame structure (2).

2. The low-vibration optical device suitable for vacuum environments according to claim 1, characterized in that, The frame structure (2) is provided with orthogonal main bars and oblique reinforcing bars arranged at a 45° angle to the orthogonal main bars. The orthogonal main bars and oblique reinforcing bars together form a composite grid topology skeleton. The composite grid topology skeleton includes multiple square grid units. Each square grid unit is further divided into triangular high-rigidity support units by oblique reinforcing bars.

3. The low-vibration optical device suitable for vacuum environments according to claim 1, characterized in that, The optical plate (1) and the frame structure (2) are welded together to form an integrated box structure. The overall shape of the integrated box structure is a regular octagon. The threaded hole array is evenly distributed on the surface of the optical plate (1), including a threaded segment set on the upper surface of the optical plate (1) and an exhaust hole connected to the threaded segment. The exhaust hole penetrates the optical plate (1).

4. A low-vibration optical device suitable for vacuum environments according to claim 1, characterized in that, The counterweight (3) is a concave structure that is narrow at the top and wide at the bottom. Multiple counterweights (3) are set in the bottom outer area of ​​the frame structure (2) and are arranged symmetrically about the geometric center of the optical device. The counterweights (3) are detachably connected to the frame structure (2) by vacuum-compatible fasteners to reduce the overall center of gravity of the optical device and suppress rigid body pitch and roll mode vibrations.

5. A low-vibration optical device suitable for vacuum environments according to claim 1, characterized in that, The support leg (4) includes an upper support section, a middle cylindrical connecting section and a bottom flange connecting section; the top surface of the upper support section is in contact with the bottom surface of the frame structure (2) and provides support; the bottom flange connecting section is fixedly connected to the vacuum chamber bottom plate by a vacuum-compatible fastener; the vacuum-compatible fastener has an exhaust channel running through it along the axial direction.

6. A design method for a low-vibration optical device suitable for a vacuum environment based on any one of claims 1 to 5, characterized in that, Includes the following steps: Step 1, establish a three-dimensional finite element solid model: according to the preset geometric configuration parameters, construct a three-dimensional finite element solid model including optical plate (1), frame structure (2), counterweight (3) and support leg (4), and assign corresponding elastic modulus, Poisson's ratio, density and isotropic loss factor according to the actual material properties; Step 2, establish ground constraint boundary conditions: apply a rigid connector to the bottom of the outrigger (4), constrain the rotational degrees of freedom of the rigid connector around the X-axis, Y-axis and Z-axis, and apply additional mass and corresponding moment of inertia to the rigid connector to construct an equivalent large mass base, and realize the equivalent simulation of the ground rigid boundary conditions through the inertial effect; Step 3, Modal characteristic analysis: Perform characteristic frequency analysis on the three-dimensional finite element solid model to obtain the natural frequencies and corresponding mode shapes of the optical device, and determine the main vibration mode characteristics of the optical device; Step 4, Constructing a ground vibration excitation model: Based on the frequency domain dynamic relationship, the measured ground vibration displacement amplitude spectral density is calculated. The equivalent power spectral density is converted into the equivalent power spectral density acting on the ground equivalent boundary conditions. This equivalent power spectral density is then applied to the ground equivalent boundary conditions to establish a stochastic vibration analysis model. The expression is: ； Where m is the equivalent mass corresponding to the ground equivalent boundary conditions. It is frequency; Step 5, Solve for random vibration response: Based on the modal characteristic analysis results, solve the frequency domain response of the random vibration analysis model to obtain the vibration response of the optical device under ground vibration excitation. Step 6, extract and evaluate vibration transmission characteristics: extract the vibration response amplitude spectrum density at the target measurement position of the optical plate (1), and compare and analyze it with the input ground vibration displacement amplitude spectrum density to obtain the vibration transmission characteristics of the optical device; Step 7, parameter optimization and design scheme determination: determine whether the vibration transmission characteristics meet the preset low vibration index requirements; if they meet the requirements, the current geometric configuration parameters are determined as the final design scheme; if they do not meet the requirements, the shape, mass and installation position of the counterweight (3) or the shape and width of the frame structure (2) are modified, and the modeling and calculation are repeated in step 1 until the index is met, and the design of the optical device is completed.

Images