Cryogenic lens low stress adhesive free elastomeric support structure

Abstract

The application discloses a low-stress and non-adhesive elastic supporting structure for a cryogenic lens, which comprises a lens frame, pre-tightening springs, adhesive pads, adjusting pads, a bottom plate and an elastic pressing plate. The pre-tightening springs are arranged on the inner side of the lens frame and are uniformly distributed in the circumferential direction. The adjusting pads are arranged between the pre-tightening springs and the lens frame. The adhesive pads are trimmed into a required shape and are adhered to the contact surface of the pre-tightening springs and the lens. The bottom plate, on which the adhesive pads for axially supporting the lens are adhered, is installed on the lens frame after solidification. The lens is placed in the lens frame and is axially supported by the bottom plate and is radially compressed and fixed by the pre-tightening springs. The elastic pressing plate is installed on the lens frame to axially position the lens in the lens frame. The pre-tightening force provided by the low-rigidity elastic unit preloading deformation is adopted to axially position the lens in the lens frame, the gravity in the ground adjustment test and the acceleration overload force in the launching process are overcome, the thermal stress caused by the thermal deformation difference is unloaded through the rigidity design of the elastic unit, and the surface shape precision of the lens at low temperature is ensured.

Description

Technical Field

[0001] This invention relates to a low-stress, adhesive-free viscoelastic support structure for cryogenic lenses, belonging to the field of cryogenic optics technology. Background Technology

[0002] With the development of space infrared remote sensors, their spectral range has expanded from near-infrared (around 1 μm) to far-infrared (around 240 μm), and even to the submillimeter wave band (670 μm). However, since current infrared detection devices have approached or reached the background detection limit, the detection sensitivity and dynamic range of infrared remote sensors are mainly limited by the magnitude of radiated noise in the observation background. Even with good external stray light suppression, their detection capability is significantly affected because the internal radiation of the optical lens components has become the main source of background radiated noise. Therefore, to reduce internal thermal radiation, lower the background noise of the infrared detector, and effectively improve the detection sensitivity and spatial resolution of infrared remote sensors, a cryogenic optical system with lens cooling must be adopted.

[0003] When a cryogenic optical system transitions from room temperature (manufacturing, assembly, and adjustment) to cryogenic operating temperature, for transmissive infrared remote sensors, the coefficients of thermal expansion (CTE) of the lens and the support structure generally differ significantly. This difference in CTE between materials causes structural distortion and deformation, affecting the positioning and surface accuracy of optical elements, leading to image quality degradation or even damage. Therefore, the design of the support structure for transmissive cryogenic lenses must not only meet high rigidity requirements but also consider the thermal effects of the lens in the cryogenic environment. Meeting the mechanical and thermal performance requirements of cryogenic lenses is a key focus of the support structure design, especially considering the adhesive properties between the lens and the support structure when reducing the operating temperature to around 100K.

[0004] Commonly used solutions for supporting transmissive cryogenic lenses rely on radially flexible structures to unload excess stress, combined with adhesive bonding techniques. Both domestic and international cryogenic lens designs employ similar design principles: rationally designing and adjusting to simultaneously meet the mechanical and thermal performance requirements of the cryogenic lens. However, for materials with poor surface hardness (such as ZnSe), micro-damage is easily left on the surface after optical processing. The maximum allowable working stress at these micro-damage locations is difficult to estimate. When bonded with cryogenic adhesives, the bonded surface is prone to stress concentration at these micro-damage locations, leading to breakage. This paper proposes a new method that uses the preload deformation of low-stiffness elastic units to provide preload force for lens positioning within the lens frame, replacing adhesive bonding and overcoming the gravity during ground assembly and testing, as well as the acceleration overload during launch.

[0005] The near-infrared spectrometer and photometer (NISP) of the European Space Agency's Euclid space telescope uses a flexible cantilever support structure with adhesive bonding technology. However, the resulting adhesive stress severely damaged the surface level of the lens and caused localized lens breakage.

[0006] Chinese invention patent CN105005132B discloses an infrared low-temperature lens structure that can only support low-temperature lenses at around 273K. It uses adhesive for fixation and compensates for the thermal deformation difference between the lens and the support structure by designing the adhesive thickness. However, the design of the adhesive thickness has certain limitations. When the adhesive is too thick, it will lead to a decrease in strength and will not be able to play a positioning role for the lens. Therefore, it is only suitable for situations where the thermal deformation difference between the lens and the structure is small. It will not be suitable for supporting lenses with temperature differences of more than 20K.

[0007] Chinese invention patent CN116107053A discloses a dual-material infrared low-temperature lens structure that uses a combination of a low-rigidity structure and a thermal matching structure to achieve thermal deformation compensation for a temperature difference of 150K. However, it still requires adhesive fixation. At an operating temperature of around 100K, it poses a high processing difficulty for materials with poor surface hardness, such as ZnSe. There is a risk that stress concentration can easily occur at micro-damage points after the adhesive surface is subjected to stress at low temperatures, leading to breakage. Summary of the Invention

[0008] The technical problem solved by this invention is to overcome the shortcomings of the prior art and provide a low-stress, adhesive-free viscoelastic support structure for cryogenic lenses, which solves the support and positioning of transmissive lenses in cryogenic environments and can be used for low-stress support and positioning of brittle lens materials in cryogenic environments.

[0009] The technical solution adopted in this invention is as follows:

[0010] A low-stress, adhesive-free elastic support structure for a cryogenic lens includes: a lens frame, a preload spring, a rubber pad, an adjustment shim, a base plate, and an elastic pressure plate.

[0011] The frame is used to mount the lens and provide an external interface. The preload spring is installed inside the frame and is evenly distributed around the circumference. An adjustment shim is provided between the preload spring and the frame.

[0012] The rubber pads are trimmed into the required shape and glued to the contact surface between the preload spring and the lens. At the same time, rubber pads are also glued to the base plate used to axially support the lens. After curing, the base plate is installed on the lens frame.

[0013] The lens is placed in the frame and supported by the base plate, and is radially compressed and fixed by a pre-tightening spring; an elastic pressure plate is installed on the frame to achieve axial positioning of the lens within the frame.

[0014] Furthermore, the preload spring is used to fix the lens and to unload radial thermal stress.

[0015] Furthermore, the elastic pressure plate is used to fix the lens to achieve axial thermal stress relief.

[0016] Furthermore, the radial preload provided by the preload spring can be adjusted by adjusting the thickness of the adjusting shim.

[0017] Furthermore, before installing the adjusting shims, the rubber pads are already glued to the contact surface between the preload spring and the lens. By measuring the distance between the rubber pads and the axis of the lens frame, the thickness of the adjusting shims that need to be installed between the preload spring and the lens frame is calculated. Adjusting shims of different thicknesses are then installed on the lens frame one by one, corresponding to the adjusting springs.

[0018] Furthermore, the process of placing the lens in the frame is as follows:

[0019] After installing the adjusting shims, adjusting springs, and base plate, fix the mirror frame onto the support base. Use the adjusting table to pull the adjusting springs outward and fix their position.

[0020] Place the lens in the frame and put it on the base plate. Use a feeler gauge to adjust the distance between the positioning boss inside the frame and the outer circle of the lens to ensure that the lens is centered.

[0021] Slowly release the adjustment platform in sequence, so that the adjustment spring is compressed around the lens;

[0022] After installing the lens and adjusting spring, install the elastic pressure plate on the lens frame to ensure the lens is axially positioned within the frame.

[0023] Furthermore, the force at each mounting point of the adjusting spring on the lens is F. n :

[0024] F n = k[ξ+δcos(n*φ)]

[0025] Where k is the spring stiffness, ξ is the initial compression of the spring during installation, δ is the displacement of the lens under gravity or overload, φ is the installation angle between two adjacent springs, and n is the spring number, n=1,2,3…N, N is the number of springs.

[0026] Furthermore, for a lens of mass m, using n evenly distributed springs for radial support, neglecting the friction between the springs and the lens, the resultant force of the radial support is in equilibrium with the force on the lens, i.e.

[0027] During ground assembly and testing g is the acceleration due to gravity;

[0028] During launch, F overload This indicates the overload force that the lens experiences during launch.

[0029] Furthermore, the minimum value of the spring stiffness k min Calculated as follows:

[0030]

[0031] The δ value is selected based on the lens eccentricity tolerance.

[0032] Furthermore, the mechanical tests simulating the launch process need to consider the static overload force to ensure that the lens and spring remain in contact at all times. In this case, δ≤ξ, and the minimum preload force provided by the spring during launch overload is:

[0033]

[0034] Furthermore, the spring adopts a beam structure with fixed ends, and the spring stiffness k is calculated using the following formula:

[0035]

[0036] Where E is the elastic modulus of the material, h is the thickness of the beam element section, b is the width of the beam element section, L is the length of the beam element, and C is the correction coefficient;

[0037] When selecting spring materials, the spring stiffness k calculated according to the above formula should be k ≥ k min .

[0038] The advantages of this invention compared to the prior art are:

[0039] (1) The present invention uses the preload deformation of the low stiffness elastic unit to achieve the positioning of the lens in the lens frame, overcomes the gravity of the ground assembly and testing and the overload of the acceleration during the launch process, and achieves the unloading of thermal stress introduced by the thermal deformation difference through the stiffness design of the elastic unit, thus ensuring the surface accuracy of the lens at low temperature.

[0040] (2) The present invention uses spring preload to support the lens without adhesive, thus avoiding the risk of lens damage due to excessive adhesive stress.

[0041] (3) This invention is applicable to large temperature difference lens support below 150K.

[0042] (4) This invention is applicable to low-temperature support of lens materials with poor surface hardness. Attached Figure Description

[0043] Figure 1 This is a diagram of the low-stress, adhesive-free viscoelastic support structure component for the cryogenic lens of the present invention.

[0044] Figure 2 Schematic diagram of the added base plate thickening support structure;

[0045] Figure 3 This is a schematic diagram of the radial force state of the lens of the present invention;

[0046] Figure 4 This is a schematic diagram showing the relative positions of the preload spring and the rubber pad of the present invention;

[0047] Figure 5 This is a schematic diagram showing the relative positions of the base plate and the rubber pad of the present invention;

[0048] Figure 6 This is a schematic diagram of an elastic pressure plate; Detailed Implementation

[0049] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0050] like Figure 1 and Figure 2 As shown, the present invention proposes a low-stress, adhesive-free elastic support structure for a cryogenic lens, comprising: a lens frame 1, a pre-tensioning spring 2, a rubber pad 3, an adjusting shim 4, a base plate 5, and an elastic pressure plate 6.

[0051] The frame 1 is used to install the lens and provide an external interface. The preload spring 2 is installed inside the frame 1 and is evenly distributed along the circumference. An adjustment shim 4 is provided between the preload spring 2 and the frame 1.

[0052] like Figure 4 As shown, the adhesive pad 3 is trimmed to the required shape and glued to the contact surface between the preload spring 2 and the lens. Simultaneously, the adhesive pad 3 is also glued to the base plate 5, which axially supports the lens. After curing, the base plate 5 is installed onto the lens frame 1, as shown. Figure 4 and Figure 5 As shown;

[0053] The lens is placed in the frame 1, supported by the base plate, and radially compressed and fixed by the preload spring 2; the elastic pressure plate 6 is installed on the frame 1 to achieve axial positioning of the lens within the frame, such as... Figure 6 As shown.

[0054] The preload spring is used to fix the lens and relieve radial thermal stress. The elastic pressure plate is used to fix the lens and relieve axial thermal stress. The radial preload force provided by the preload spring 2 is adjusted by adjusting the thickness of the adjusting shim 4. Figure 3 The diagram shows the radial force state of the lens of the present invention.

[0055] Before installing the adjusting shim 4, the adhesive pad 3 has been glued to the contact surface between the preload spring 2 and the lens. By measuring the distance between the adhesive pad and the axis of the lens frame, the thickness of the adjusting shim that needs to be installed between the preload spring and the lens frame is calculated. Adjusting shims of different thicknesses are then installed on the lens frame one by one, corresponding to the adjusting spring.

[0056] The process of placing the lens in the frame is as follows: After installing the adjusting shims, adjusting springs, and base plate, fix the frame on the support base, use the adjusting table to pull the adjusting springs outwards and fix their position;

[0057] Place the lens in the frame and put it on the base plate. Use a feeler gauge to adjust the distance between the positioning boss inside the frame and the outer circle of the lens to ensure that the lens is centered.

[0058] Slowly release the adjustment platform in sequence, so that the adjustment spring is compressed around the lens;

[0059] After installing the lens and adjusting spring, install the elastic pressure plate on the lens frame to ensure the lens is axially positioned within the frame.

[0060] The force F at each mounting point of the adjusting spring on the lens n :

[0061] F n = k[ξ+δcos(n*φ)]

[0062] Where k is the spring stiffness, ξ is the initial compression of the spring during installation, δ is the displacement of the lens under gravity or overload, φ is the installation angle between two adjacent springs, and n is the spring number, n=1,2,3…N, N is the number of springs.

[0063] For a lens of mass m, radial support is provided by n uniformly distributed springs. Neglecting friction between the springs and the lens, the resultant radial support force is in equilibrium with the force acting on the lens.

[0064] During ground assembly and testing g is the acceleration due to gravity;

[0065] During launch, F overload This indicates the overload force that the lens experiences during launch.

[0066] Minimum value of spring stiffness k min Calculated as follows:

[0067]

[0068] The δ value is selected based on the lens eccentricity tolerance.

[0069] This invention considers the static overload force to ensure that the lens and spring always remain in contact, and provides the minimum preload force that can be provided during launch overload. The value of the preload force must meet the mechanical resistance requirements while also ensuring the accuracy of the lens surface shape.

[0070] The mechanical test simulating the launch process needs to consider the static overload force to ensure that the lens and spring remain in contact at all times. Under this condition, δ≤ξ. The minimum preload force provided by the spring during launch overload is:

[0071]

[0072] The spring uses a beam structure with fixed ends, and the spring stiffness k is calculated using the following formula:

[0073]

[0074] Where E is the elastic modulus of the material, h is the thickness of the beam element section, b is the width of the beam element section, L is the length of the beam element, and C is the correction coefficient;

[0075] When selecting spring materials, the spring stiffness k calculated according to the above formula should be k ≥ k min .

[0076] Example:

[0077] The elastic support structure described in this invention is assembled in the following order:

[0078] 1. Trim the rubber pad into the desired shape and glue it to the contact surface between the spring and the lens;

[0079] 2. Install the spring onto the lens frame, measure the distance between the rubber pad and the fitted axis of the lens frame using a coordinate measuring machine, and calculate the thickness value of the adjustment shim between the spring and the lens frame based on this dimension. Install the shims of different thicknesses and the spring assembly one by one onto the lens frame.

[0080] 3. Attach the adhesive pad to the base plate, and after it has cured, install the base plate onto the lens frame;

[0081] 4. Fix the lens frame with the shims, springs, and base plate installed on the support base. Use the adjustment table to pull the spring outward and fix its position. Gently place the lens into the frame and place it on the base plate. Use a feeler gauge to adjust the distance between the positioning boss inside the lens frame and the outer circle of the lens to ensure that the lens is centered. Then slowly release the adjustment table in sequence, so that the spring is in a compressed state around the lens.

[0082] 5. After installing the lens and spring, install an elastic pressure plate on the lens frame to ensure the lens is axially positioned within the frame.

[0083] The parts of this invention not described in detail are common knowledge to those skilled in the art.

Claims

1. A low-stress, adhesive-free viscoelastic support structure for cryogenic lenses, characterized in that... include: The frame (1), pre-tension spring (2), rubber pad (3), adjusting shim (4), base plate (5) and elastic pressure plate (6); The frame (1) is used to install the lens and provide an external interface. The preload spring (2) is installed inside the frame (1) and is evenly distributed along the circumference. An adjustment shim (4) is provided between the preload spring (2) and the frame (1). The adhesive pad (3) is trimmed into the required shape and glued to the contact surface between the preload spring (2) and the lens. At the same time, the adhesive pad (3) is also glued to the base plate (5) used to support the lens axially. After curing, the base plate (5) is installed on the lens frame (1). The lens is placed in the frame (1), supported by the base plate, and compressed and fixed radially by the pre-tightening spring (2); the elastic pressure plate (6) is installed on the frame (1) to realize the axial positioning of the lens in the frame; Preload springs are used to fix the lens and to unload radial thermal stress; The elastic pressure plate is used to fix the lens and relieve axial thermal stress. The radial preload provided by the preload spring (2) is adjusted by adjusting the thickness of the adjusting shim (4); Before installing the adjusting shim (4), the rubber pad (3) has been glued to the contact surface between the preload spring (2) and the lens. By measuring the distance between the rubber pad and the axis of the frame fitting, the thickness value of the adjusting shim that needs to be installed between the preload spring and the frame is calculated. Adjusting shims of different thicknesses are installed on the lens frame one by one with the adjusting spring. The process of placing the lens in the frame is as follows: After installing the adjusting shims, adjusting springs, and base plate, fix the mirror frame onto the support base. Use the adjusting table to pull the adjusting springs outward and fix their position. Place the lens in the frame and put it on the base plate. Use a feeler gauge to adjust the distance between the positioning boss inside the frame and the outer circle of the lens to ensure that the lens is centered. Slowly release the adjustment platform in sequence, so that the adjustment spring is compressed around the lens; After installing the lens and adjusting spring, install the elastic pressure plate on the lens frame to ensure the axial positioning of the lens within the lens frame; The force at each mounting point of the adjusting spring on the lens is : Where k is the spring stiffness. φ is the initial compression of the spring during installation, δ is the displacement of the lens under gravity or overload, φ is the installation angle between two adjacent springs, and n is the spring number, n=1,2,3…N, N is the number of springs; For a lens of mass m, radial support is provided by n uniformly distributed springs. Neglecting friction between the springs and the lens, the resultant radial support force is in equilibrium with the force acting on the lens. During ground assembly and testing g is the acceleration due to gravity; During launch F overload This indicates the overload force that the lens experiences during launch; Minimum value of spring stiffness Calculated as follows: The δ value is selected based on the lens eccentricity tolerance; The mechanical test simulating the launch process needs to consider the static overload force to ensure that the lens and spring remain in contact at all times, where δ≤ The minimum preload force provided by the spring during launch overload is: ； The spring uses a beam structure with fixed ends, and the spring stiffness k is calculated using the following formula: Where E is the elastic modulus of the material, h is the thickness of the beam element section, b is the width of the beam element section, L is the length of the beam element, and C is the correction coefficient; When selecting spring materials, the spring stiffness k calculated according to the above formula is greater than or equal to 1. .

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