Lens gluing anti-displacement process based on gradient adhesive layer and temperature field cooperation

Abstract

This invention relates to the field of optical lens bonding technology, and in particular to a lens bonding anti-displacement process based on the synergy of gradient adhesive layers and temperature fields. The process includes: coating a base layer and a top layer of adhesive to form a gradient adhesive layer on the bonding surface of a first lens; applying an axial compressive force to overcompress the adhesive layer after bonding a second lens; maintaining the overcompressed state and implementing gradient heating from the center to the outer edge, while simultaneously applying high-frequency micro-amplitude shear vibration in the planar direction to thin the adhesive layer in the planar direction while constraining its thickness; monitoring the relative displacement of the lenses and dynamically adjusting the heating power; continuing to heat the adhesive layer after stopping the vibration to completely cure it under the overcompressed state; releasing the compressive force to allow the adhesive layer to elastically rebound and establish pre-tension stress; and synchronously and slowly cooling the entire assembly. This pre-tension stress and the cooling shrinkage stress counteract each other, fundamentally eliminating the problems of hot alignment and cold misalignment. The optical axis misalignment is controlled at the sub-micron level, making it suitable for bonding precision lens assemblies such as optical microscope objectives.

Description

Technical Field

[0001] This invention relates to the field of optical lens bonding technology, and in particular to a lens bonding anti-displacement process based on the synergy of gradient adhesive layer and temperature field. Background Technology

[0002] The imaging quality of an optical microscope is highly dependent on the assembly precision of optical components such as the objective lens, condenser lens, and eyepiece. The objective lens, as the core imaging component of the microscope, is typically composed of multiple lenses with different curvatures and refractive indices bonded together with an optical adhesive layer to correct geometric aberrations such as spherical aberration, chromatic aberration, and astigmatism. The coaxiality of the optical axis, the spacing between the lenses, and the uniformity of the adhesive layer thickness directly determine the objective lens's resolution, numerical aperture, and imaging contrast. In current optical microscope objective lens manufacturing, thermosetting optical adhesive is commonly used to bond two or more lenses into a cemented lens assembly. The specific process involves uniformly applying optical adhesive to the bonding surface of the first lens, attaching the second lens, and then heating the entire assembly to cure and set the adhesive layer. However, this process has inherent technical flaws. During the bonding process, the adhesive layer softens upon heating, and the lens is in an adjustable, suspended state. At this point, high-precision positioning can be achieved through mechanical alignment. However, once the adhesive layer is fully cured and cooled to room temperature, it undergoes chemical and thermal shrinkage. Furthermore, the difference in thermal expansion coefficients between the adhesive layer and the lens substrate leads to micron-level or even submicron-level shifts in the relative position of the lens after cooling and setting. For high-magnification objectives, this shift is sufficient to cause optical axis deviation and excessive aberrations, resulting in blurred image edges or distorted color reproduction. In addition, during the alignment stage before curing, the adhesive layer needs to maintain appropriate fluidity to allow for fine-tuning of the lens in the horizontal plane. However, if the fluidity is too high, the vertical support stiffness of the adhesive layer is insufficient, making it easy for the lens to tilt or slip during bonding, resulting in uneven adhesive layer thickness. If the fluidity of the adhesive layer is reduced to increase the support stiffness, the resistance to fine-tuning in the horizontal plane increases, making it difficult to achieve submicron-level alignment accuracy. The existing technology fails to simultaneously meet the dual requirements of free fine-tuning in the horizontal plane and stable support in the vertical direction. Regarding shrinkage stress management, in existing thermosetting processes, the adhesive layer shrinks isotropically during curing and cooling. Since the adhesive layer and lens are rigidly bonded in the horizontal plane, the volume shrinkage of the adhesive layer directly translates into a drag force on the lens, causing irreversible displacement of the aligned lens position. Existing technologies either rely on external mechanical clamps for forced positioning, but clamping stress can easily damage the lens surface or introduce additional stress birefringence. Alternatively, methods such as uniform heating or simple stepped temperature increases can only slow down the shrinkage rate to a certain extent, failing to fundamentally change the physical mechanism by which the shrinkage stress of the adhesive layer is passively transferred to the lens. More importantly, existing thermosetting bonding processes passively bear the shrinkage of the adhesive layer without constructing a pre-stress field within the adhesive layer to actively counteract subsequent cooling shrinkage. During the transition of the adhesive layer from liquid to solid, the shrinkage behavior of the molecular chains develops completely freely, without any built-in mechanical compensation mechanism to balance the internal stress generated by shrinkage.

[0003] Therefore, there is an urgent need for a bonding process that can actively build a prestress compensation field inside the adhesive layer, while taking into account high-precision horizontal alignment and stable vertical support, and fundamentally eliminate lens displacement after cooling and shaping, so as to meet the assembly requirements of precision optical components such as high-magnification objectives of optical microscopes. Summary of the Invention

[0004] This invention aims to at least solve the technical problems existing in the prior art, and in particular, it innovatively proposes a lens bonding anti-displacement process based on the synergy of gradient adhesive layer and temperature field.

[0005] To achieve the above-mentioned objectives of this invention, this invention provides a lens bonding anti-displacement process based on the synergy of gradient adhesive layer and temperature field, comprising the following steps: S1, providing a first lens and a second lens, applying a base layer adhesive to the bonding surface of the first lens, and applying a top layer adhesive on top of the base layer adhesive, the base layer adhesive and the top layer adhesive forming a gradient adhesive layer; S2, the second lens bonding surface is bonded to the surface adhesive to form a lens assembly; S3, apply axial compressive force to the lens group, so that the gradient adhesive layer is compressed in the thickness direction to an overcompressed state less than its designed thickness, and the thickness of the overcompressed state is 50% to 70% of the designed thickness; S4. While maintaining the overcompression state, gradient heating is applied to the gradient adhesive layer from the center to the outer edge, and high-frequency micro-amplitude shear vibration in the planar direction is applied to the lens group, so that the gradient adhesive layer produces a shear thinning effect in the planar direction while maintaining high viscosity constraint in the thickness direction. The frequency of the high-frequency micro-amplitude shear vibration is 20kHz~40kHz and the amplitude is 0.1μm~0.5μm. S5. During the gradient heating process, the relative displacement between the first lens and the second lens is monitored. When the relative displacement exceeds the preset threshold, the heating power of the corresponding area is dynamically adjusted to suppress the displacement trend in the opposite direction. S6, turn off the high-frequency micro-amplitude shear vibration and maintain the axial compressive force, continue to heat up so that the gradient adhesive layer is completely cured under overcompression. After the gradient adhesive layer is cured, it forms an anisotropic adhesive layer with pre-tension stress in the thickness direction and high modulus locking structure in the planar direction. S7. After the gradient adhesive layer is fully cured, release the axial compressive force so that the gradient adhesive layer can elastically rebound to the designed thickness. The pre-tension stress and the thermal shrinkage stress and chemical shrinkage stress of the adhesive layer during the subsequent cooling process are inversely offset. S8, using a slow cooling temperature lower than the highest temperature of the curing stage, to synchronously cool the entire lens assembly, so that the first and second lenses are cooled to room temperature while in the set state.

[0006] Optionally, the thickness of the bottom layer adhesive is 30% to 50% of the total thickness of the gradient adhesive layer, and the thickness of the top layer adhesive is 50% to 70% of the total thickness of the gradient adhesive layer.

[0007] Optionally, the underlayer adhesive contains a positive thermal expansion coefficient tackifying nanofiller, which is silica nanoparticles or alumina nanoparticles with a particle size of 10nm~100nm, and its mass fraction in the underlayer adhesive is 5%~15%.

[0008] Optionally, the topcoat adhesive is a pure adhesive without added nanofillers, or contains silica nanoparticles with a mass fraction not exceeding 3%.

[0009] Optionally, in step S3, the axial compressive force is 2N~8N, so that the gradient adhesive layer is compressed to 55%~65% of the designed thickness.

[0010] Optionally, in step S4, the gradient heating adopts concentric ring-shaped partitioned heating, which is divided into at least a central heating zone, an intermediate heating zone and an outer edge heating zone, with a heating power ratio of 1.2~1.5:1:0.6~0.8; high-frequency micro-amplitude shear vibration is applied to the radial or tangential direction of the lens group through a piezoelectric ceramic transducer.

[0011] Optionally, in step S5, the relative displacement is monitored using a non-contact optical displacement sensor, with a preset threshold of 0.01% to 0.05% of the lens diameter.

[0012] Optionally, in step S6, the heating rate is as follows: 2°C / min to 5°C / min in the central region, 1°C / min to 3°C / min in the middle region, and 0.5°C / min to 1.5°C / min in the outer region. The temperature for complete curing is 110°C to 140°C, and the curing time is 20 min to 40 min.

[0013] Optionally, in step S7, after releasing the axial compressive force, the elastic rebound of the gradient adhesive layer is 30% to 50% of the designed thickness, and the pre-tension stress is 0.5 MPa to 3 MPa.

[0014] Optionally, in step S8, the slow cooling temperature is 20°C~40°C lower than the highest temperature of the curing stage, the slow cooling rate is 0.5°C / min~2°C / min, and the slow cooling time is not less than 30 min; and the gradient adhesive layer is not exposed to ultraviolet light throughout the entire heat curing and slow cooling process.

[0015] The beneficial effect of the present invention is that by pre-compression and curing, a pre-tension stress field in the thickness direction is actively constructed inside the adhesive layer. During the cooling process, the pre-tension stress cancels out the chemical shrinkage stress and thermal shrinkage stress of the adhesive layer in real time. This transforms the passive shrinkage drag in the traditional process into active pre-stress self-compensation, fundamentally eliminating the net stress that causes lens displacement and significantly improving the optical axis stability of the cemented lens group.

[0016] This invention applies high-frequency micro-amplitude shear vibration in a planar direction under overcompression. Utilizing the thinning effect of the adhesive layer under shear, the lens can be freely fine-tuned in the horizontal plane to achieve sub-micron level alignment. Simultaneously, the thickness direction maintains high viscosity constraint under axial compressive force to ensure vertical positional stability. This mechanism simultaneously satisfies the dual requirements of high-precision horizontal alignment and stable vertical support, overcoming the bottleneck of the traditional process where fluidity and support stiffness cannot be simultaneously achieved. This invention uses gradient heating to cure the adhesive layer zone by zone from the center outwards. The central region cures first to form a reference positioning area, while the outer regions cure later, releasing their shrinkage stress to the free boundary. This avoids dragging the already positioned central region and works synergistically with the pre-tension stress compensation mechanism to further suppress lens displacement after cooling and shaping.

[0017] This invention introduces displacement closed-loop monitoring and dynamic power adjustment during the curing process. When a displacement trend is detected, the curing rate is changed by adjusting the heating power of the corresponding area, forming a curing rate difference to generate a reverse constraint force. This moves the correction window forward to the curing stage instead of post-inspection and rework, significantly improving process stability and yield.

[0018] This invention does not rely on special functional fillers such as negative thermal expansion ceramics or magnetic particles. It can achieve anti-displacement simply by controlling the mechanical timing. It is applicable to conventional thermosetting optical adhesives, has a wide process window, controllable cost, and is easy to implement industrially in the bonding and assembly of precision optical components such as optical microscope objectives.

[0019] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0020] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a schematic diagram of the lens bonding anti-displacement process based on the synergy of gradient adhesive layer and temperature field described in this invention. Detailed Implementation

[0021] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0022] Example 1, This embodiment provides a lens bonding anti-displacement process based on the synergy of gradient adhesive layer and temperature field, used for bonding and assembling two plano-convex lenses in a 100× oil immersion objective lens of an optical microscope.

[0023] The first and second lenses were selected. Both lenses are optical glass plano-convex lenses with a diameter of 8 mm, a center thickness of 2.3 mm, a radius of curvature R1 = 1.85 mm, and are made of H-K9L material. A base coat of adhesive was applied to the planar side of the bonding surface of the first lens using a spin-coating method at a speed of 1200 rpm, resulting in a base coat thickness of 18 μm. This base coat is a thermosetting epoxy resin optical adhesive (refractive index 1.52, curing shrinkage 3.2%), containing 10% by mass of silica nanoparticles (particle size 50 nm, positive thermal expansion coefficient approximately 0.5 × 10⁻⁻⁻⁻⁶). 6 / ℃) as a thickening nanofiller with a positive coefficient of thermal expansion. A topcoat was applied over the base coat using a spin-coating method at 800 rpm, resulting in a topcoat thickness of 27 μm. This topcoat was a pure adhesive with the same matrix as the base coat, without any added nanofillers. Thus, the base coat and topcoat formed a gradient adhesive layer with a total designed thickness of 45 μm, where the base coat accounted for 40% of the total thickness and the topcoat accounted for 60%.

[0024] The second lens is bonded to the surface adhesive to form a lens assembly. During bonding, a six-axis precision alignment stage is used for coarse alignment to ensure that the optical axis deviation between the two lenses is less than 5μm. An axial compressive force of 5N is applied to the lens assembly through a precision pressure loading mechanism, which compresses the gradient adhesive layer to 27μm in the thickness direction, i.e., to 60% of the designed thickness, which is an overcompression state. At this time, the adhesive layer molecular chains are forced to be highly oriented and densely packed in the thickness direction.

[0025] While maintaining this overcompression state, the lens assembly is placed on a zoned heating fixture. This fixture has concentric ring-shaped heating units, divided into a central heating zone (4 mm in diameter), an intermediate heating zone (4-6 mm in diameter), and an outer edge heating zone (6-8 mm in diameter). Zoned heating is initiated, with a heating power ratio of 1.3:1:0.7. The heating rate is 3°C / min for the central region, 2°C / min for the intermediate region, and 1°C / min for the outer edge region, allowing the gradient adhesive layer to be heated zone by zone from the center outwards. Simultaneously, high-frequency micro-amplitude shear vibration in the planar direction is applied by piezoelectric ceramic transducers mounted on both radial sides of the lens assembly. This shear vibration has a frequency of 30 kHz and an amplitude of 0.3 μm. Under these conditions, the adhesive layer undergoes shear thinning in the planar direction, reducing the apparent viscosity. The lens can be freely fine-tuned in the horizontal plane for precise alignment; the thickness direction maintains high viscosity due to axial compressive force, and the vertical position remains stable.

[0026] The relative displacement of the two lenses is monitored in real time using a non-contact optical displacement sensor (0.01 μm resolution, 1 kHz sampling frequency). The preset threshold is 0.03% of the lens diameter, or 2.4 μm. When a displacement trend is detected towards a certain heating area, the heating power in that area is reduced by 0.2 W to delay the curing of the adhesive layer on that side, while the heating power on the side with the opposite displacement direction is increased by 0.15 W to create a curing rate difference and generate a reverse constraint force.

[0027] High-frequency micro-amplitude shear vibration was turned off, and the axial compression force was maintained at 5N. The temperature was then increased to the complete curing temperature of 120°C, with a curing time of 30 minutes. During this process, the heating rate was maintained at 3°C / min in the central region, 2°C / min in the middle region, and 1°C / min in the outer region. The adhesive layer completed cross-linking and curing under overcompression geometry. The cross-linking network locked the molecular chains in a densely oriented conformation along the thickness direction, forming an anisotropic adhesive layer with pre-tension in the thickness direction and a high-modulus locked structure in the planar direction. No ultraviolet light was applied during the entire thermosetting and slow cooling process.

[0028] After the gradient adhesive layer has fully cured, the axial compressive force is released, and the gradient adhesive layer elastically rebounds to the designed thickness of 45 μm, with an elastic rebound of 40% of the designed thickness, i.e., 18 μm. A stable pre-tension stress in the thickness direction is established within the adhesive layer, which is approximately 2 MPa. The lens assembly is then subjected to overall synchronous cooling at a slow cooling temperature of 90°C (30°C lower than the maximum curing temperature) at a rate of 1°C / min for 40 minutes. During the cooling process, the adhesive layer undergoes chemical and thermal shrinkage, and the shrinkage stress cancels out the previously established pre-tension stress. Since the planar direction has returned to a high-modulus locked state after the shear vibration is turned off, there is no displacement in the planar direction; the shrinkage in the thickness direction is compensated by the pre-tension stress, and the net stress in the thickness direction approaches zero, ultimately allowing the first and second lenses to cool to room temperature in a shaped state.

[0029] The optical axis offset of the cemented lens assembly was measured using a laser interferometer, and the result was 0.4 μm. The uniformity of the adhesive layer thickness was measured using a white light interferometer, with a deviation of ±0.8 μm. The residual stress of the adhesive layer was measured using a stress birefringence meter. The stress in the planar direction was almost zero, while the stress in the thickness direction showed a gradient distribution, and the net stress after pre-tensioning was less than 0.3 MPa. These results indicate that the optical axis offset in this embodiment is controlled at the sub-micron level, meeting the stringent requirements of the 100× oil immersion objective lens for bonding accuracy (optical axis offset << 1 μm).

[0030] Example 2, This embodiment is a comparative example. Its lens material, size, type of optical adhesive and design thickness are exactly the same as those in Example 1. The difference is that it does not use the gradient adhesive layer, overcompression pre-setting, shear vibration and gradient heating technology of the present invention, but uses the existing conventional thermosetting adhesive process.

[0031] Specifically, a homogeneous optical adhesive (with the same formulation as the topcoat adhesive in Example 1, but without added nanofillers) was uniformly coated onto the bonding surface of the first lens, with an adhesive layer thickness of 45 μm. After the second lens was attached, a light pressure of 0.5 N was applied to maintain its position. The lens assembly was placed in an integrated oven and heated to 120°C at a uniform rate of 2°C / min, held at that temperature for 30 min, and then cooled to room temperature in the oven. Throughout the curing process, no axial compression force was applied, there was no overcompression, no shear vibration, no zoned gradient heating, and no real-time displacement monitoring or dynamic adjustment.

[0032] The same testing equipment as in Example 1 was used for measurement, and the results are as follows: the optical axis offset is 6.2 μm, the uniformity deviation of the adhesive layer thickness is ±4.5 μm, there are obvious shrinkage and drag marks at the interface between the adhesive layer and the lens, and a 0.8 μm thick adhesive layer thinning area appears at the edge. This offset is more than 15 times that of Example 1, and the offset direction is irregular, which cannot meet the assembly requirements of the 100× oil immersion objective lens, requiring rework or scrapping.

[0033] Example 3, This embodiment is a comparative example with some missing features. Its lens, adhesive layer material and design thickness are the same as those in Example 1. It also applies a 5N axial compression force to overcompress the adhesive layer to 27μm, but turns off the high-frequency micro-amplitude shear vibration and uses overall uniform heating instead of partitioned gradient heating. Other conditions are the same as those in Example 1.

[0034] Specifically, under over-compression conditions without applying 30kHz shear vibration, the lens assembly cannot be freely fine-tuned in the horizontal plane through the shear thinning effect. After bonding, the optical axis deviation remains at 4.5μm, the level during the coarse alignment stage, and cannot be further corrected. Simultaneously, an overall oven is used to uniformly heat to 120°C at a rate of 2°C / min, without a gradient curing sequence from the center to the outer edge; the adhesive layer cures synchronously throughout, and shrinkage stress is transmitted to both the center and edges simultaneously. After curing, the compressive force is released and the lens is slowly cooled.

[0035] Test results: The optical axis offset was 3.8 μm, which is lower than that of the conventional process in Example 2 (due to the pre-existing pre-stress from over-compression), but still about 9 times higher than that of the complete process in Example 1. The uniformity deviation of the adhesive layer thickness was ±3.2 μm, and due to the lack of shear vibration-assisted leveling, several wavy defects with uneven thickness remained in the adhesive layer. These results indicate that over-compression alone, without the synergistic effect of shear vibration and gradient heating, cannot simultaneously achieve high-precision horizontal alignment and directional stress release, resulting in limited offset suppression.

[0036] Example 4, The difference between this embodiment and Embodiment 1 is that the bottom adhesive is a thermosetting modified acrylic optical adhesive, in which 12% by mass of alumina nanoparticles (30nm in diameter) are added as a positive thermal expansion coefficient thickening nanofiller. The top adhesive is a pure adhesive of the same matrix, in which 2% by mass of silica nanoparticles (20nm in diameter) are added, which conforms to the preferred range of filler types and particle sizes in claims 3 and 4. The total designed thickness of the gradient adhesive layers is 50μm, with the bottom adhesive thickness at 20μm (40%) and the top adhesive thickness at 30μm (60%). The axial compression force is 6N, and the thickness after overcompression is 32μm (64% of the designed thickness). The zone heating power ratio is 1.4:1:0.65, the complete curing temperature is 130°C, the curing time is 25min, the slow cooling temperature is 95°C (lower than the maximum curing temperature of 35°C), and the slow cooling rate is 1.5°C / min.

[0037] Test results: The optical axis offset was 0.6 μm, and the shear strength of the adhesive layer was increased by 18% compared with Example 1. This indicates that while the alumina nanoparticles improved the modulus of the underlying adhesive, they did not have a negative impact on the pre-stress compensation mechanism. This makes it suitable for objective lens bonding scenarios where the mechanical strength of the adhesive layer is required to be higher.

[0038] In summary, this invention, through the synergistic effect of various process steps including gradient adhesive layer structure design, overcompression pre-setting, high-frequency micro-amplitude shear vibration, gradient heating from the center to the outer edge, closed-loop monitoring of displacement during curing, complete curing under overcompression and elastic rebound to establish pre-tension stress, and overall synchronous slow cooling and shaping, actively constructs a pre-tension stress field in the thickness direction within the adhesive layer. This pre-tension stress cancels out the chemical shrinkage stress and thermal shrinkage stress during the cooling process in real time, fundamentally solving the technical problem of "hot alignment and cold offset" in existing thermosetting adhesive processes. As can be seen from the comparison of Examples 1 to 4, the complete process of the present invention can stably control the optical axis offset of the cemented lens assembly at the sub-micron level, which is more than an order of magnitude lower than the existing conventional overall uniform heating process, and also about an order of magnitude lower than the partial process with only over-compression without shear vibration and gradient heating. At the same time, the present invention does not rely on special functional fillers such as negative thermal expansion ceramics and magnetic particles, and can achieve anti-displacement by mechanical timing control alone. It is applicable to conventional thermosetting optical adhesives, has a wide process window, and is easy to implement industrially in the bonding and assembly of precision optical components such as optical microscope objectives.

[0039] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A lens bonding anti-displacement process based on the synergy of gradient adhesive layer and temperature field, characterized in that, Includes the following steps: S1, providing a first lens and a second lens, applying a base layer adhesive to the bonding surface of the first lens, and applying a top layer adhesive on top of the base layer adhesive, wherein the base layer adhesive and the top layer adhesive form a gradient adhesive layer; S2, the second lens bonding surface is bonded to the surface adhesive to form a lens assembly; S3, apply an axial compressive force to the lens group, causing the gradient adhesive layer to be compressed in the thickness direction to an overcompressed state less than its designed thickness, wherein the thickness of the overcompressed state is 50% to 70% of the designed thickness; S4, while maintaining the overcompression state, the gradient adhesive layer is subjected to gradient heating from the center to the outer edge, and high-frequency micro-amplitude shear vibration in the planar direction is applied to the lens group, so that the gradient adhesive layer produces a shear thinning effect in the planar direction while maintaining high viscosity constraint in the thickness direction. The frequency of the high-frequency micro-amplitude shear vibration is 20kHz~40kHz and the amplitude is 0.1μm~0.5μm. S5, during the gradient heating process, the relative displacement between the first lens and the second lens is monitored. When the relative displacement exceeds a preset threshold, the heating power of the corresponding area is dynamically adjusted to suppress the displacement trend in the opposite direction. S6, turn off the high-frequency micro-amplitude shear vibration and maintain the axial compression force, continue to heat up so that the gradient adhesive layer is completely cured under the over-compression state. After the gradient adhesive layer is cured, it forms an anisotropic adhesive layer with pre-tension stress in the thickness direction and high modulus locking structure in the planar direction. S7. After the gradient adhesive layer is fully cured, the axial compressive force is released, allowing the gradient adhesive layer to elastically rebound to the designed thickness. The pre-tension stress cancels out the thermal shrinkage stress and chemical shrinkage stress of the adhesive layer during the subsequent cooling process. S8, the lens assembly is cooled synchronously as a whole at a slow cooling temperature lower than the highest temperature of the curing stage, so that the first lens and the second lens are cooled to room temperature in the shaped state.

2. The lens bonding anti-displacement process based on the synergy of gradient adhesive layer and temperature field as described in claim 1, characterized in that, The thickness of the bottom adhesive layer is 30% to 50% of the total thickness of the gradient adhesive layer, and the thickness of the top adhesive layer is 50% to 70% of the total thickness of the gradient adhesive layer.

3. The lens bonding anti-displacement process based on the synergy of gradient adhesive layer and temperature field as described in claim 1, characterized in that, The bottom adhesive contains a positive thermal expansion coefficient thickening nanofiller, which is silica nanoparticles or alumina nanoparticles with a particle size of 10nm~100nm, and its mass fraction in the bottom adhesive is 5%~15%.

4. The lens bonding anti-displacement process based on the synergy of gradient adhesive layer and temperature field as described in claim 1, characterized in that, The surface adhesive is a pure adhesive without added nanofillers, or contains silica nanoparticles with a mass fraction not exceeding 3%.

5. The lens bonding anti-displacement process based on the synergy of gradient adhesive layer and temperature field as described in claim 1, characterized in that, In step S3, the axial compressive force is 2N~8N, which compresses the gradient adhesive layer to 55%~65% of the designed thickness.

6. The lens bonding anti-displacement process based on the synergy of gradient adhesive layer and temperature field as described in claim 1, characterized in that, In step S4, the gradient heating adopts concentric ring-shaped partitioned heating, which is divided into at least a central heating zone, an intermediate heating zone and an outer edge heating zone, with a heating power ratio of 1.2~1.5:1:0.6~0.8; the high-frequency micro-amplitude shear vibration is applied to the radial or tangential direction of the lens group through a piezoelectric ceramic transducer.

7. The lens bonding anti-displacement process based on the synergy of gradient adhesive layer and temperature field as described in claim 1, characterized in that, In step S5, the relative displacement is monitored using a non-contact optical displacement sensor, and the preset threshold is 0.01% to 0.05% of the lens diameter.

8. The lens bonding anti-displacement process based on the synergy of gradient adhesive layer and temperature field as described in claim 1, characterized in that, In step S6, the heating rate for the continued heating is: 2°C / min to 5°C / min in the central region, 1°C / min to 3°C / min in the middle region, and 0.5°C / min to 1.5°C / min in the outer region. The temperature for complete curing is 110°C to 140°C, and the curing time is 20 min to 40 min.

9. The lens bonding anti-displacement process based on the synergy of gradient adhesive layer and temperature field as described in claim 1, characterized in that, In step S7, after releasing the axial compressive force, the elastic rebound of the gradient adhesive layer is 30% to 50% of the designed thickness, and the pre-tension stress is 0.5 MPa to 3 MPa.

10. The lens bonding anti-displacement process based on the synergy of gradient adhesive layer and temperature field as described in claim 1, characterized in that, In step S8, the slow cooling temperature is 20°C~40°C lower than the highest temperature of the curing stage, the slow cooling rate is 0.5°C / min~2°C / min, and the slow cooling time is not less than 30min; and the gradient adhesive layer is not exposed to ultraviolet light during the entire heat curing and slow cooling process.

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