A lens temperature drift online testing system and method based on inverse projection

Abstract

The application discloses a lens temperature drift online test system and method based on inverse projection, and belongs to the field of optical lens detection. The system comprises a sealed dry constant temperature environment system, a lens supporting part, a TEC heating and refrigeration system, a heat conduction positioning jig, an inverse projection MTF detection system and a control module. When testing, the lens to be tested is placed in a normal pressure sealed cavity filled with dry gas, so that lens deformation caused by low temperature frosting and negative pressure is avoided. The system builds a low expansion physical reference datum which is not interfered by local temperature change through an inwall water cooling temperature control Invar mounting plate and a quartz glass supporting part. The control module controls the TEC to adjust the temperature of the lens, and drives a motor to drive the reticle to scan the defocus parabola to find the MTF peak value. Since the datum is constant, the difference between the absolute coordinates of the motor corresponding to the MTF peak values at different temperatures can be directly calculated one by one to calculate the back focus change of the lens. The application realizes one-stop high-precision online testing, is uniformly heated, and greatly reduces the equipment cost.

Description

[Technical Field] This invention belongs to the field of optical lens testing technology, specifically relating to an online lens temperature drift testing system and method based on inverse projection. [Background Technology] With the development of ADAS technology in the automotive industry, the gradual popularization of L2 and L3 assisted driving, and the breakthrough of L4 fully autonomous driving technology, camera modules used in automobiles are becoming increasingly important. Automobiles operate under complex conditions, with ambient temperatures generally ranging from -40℃ to 120℃. The internal structure of the camera module, the thermal expansion and contraction of the lenses, and the changes in the lens refractive index at different temperatures can all cause the lens to lose focus in extreme high and low temperature environments, even though it is clear at room temperature. This leads to changes in MTF and depth of field, seriously affecting the safety of autonomous driving. Therefore, objectively and accurately measuring the temperature drift effect of imaging lenses is crucial for the temperature drift compensation design of lenses and camera modules.

[0003] The current industry standard for temperature drift testing involves using an MTF meter to detect the mechanical back focus position and MTF peak value at room temperature, then placing the lens in a high-temperature oven for a period of time before quickly placing it into the instrument for testing. During the process of removing the lens from the oven and placing it into the instrument, the lens casing temperature drops rapidly, making it impossible to accurately reflect the actual high-temperature state of the lens. In addition, removing the lens from a sub-zero environment to a room temperature environment will inevitably cause frost to form on the lens, making this method unsuitable for measuring low-temperature changes.

[0004] Existing foreign lens temperature drift testing equipment addresses the low-temperature frosting problem by adding a sealed cavity and evacuating the MTF measuring instrument, and using TEC to control the temperature of the bottom metal tray. However, this approach is extremely costly because the heating plate expands and contracts with temperature changes. The equipment must place a reference glass inside the cavity and relies on an extremely expensive air gap measuring instrument to indirectly measure back focal length changes. Secondly, automotive-mounted sealed lenses are designed to be waterproof and airtight; evacuating the vacuum creates negative pressure, causing lens deformation and changes in lens structure, resulting in inaccurate measurement results. Thirdly, the lens only contacts the heating plate at the bottom, resulting in a small contact area. This uneven heating, especially when measuring telephoto lenses with high optical length, leads to inaccurate measurement results. [Summary of the Invention] In order to solve the technical problems existing in the prior art, such as lens deformation due to vacuuming, high cost of measuring equipment, low temperature frosting, and uneven heating of telephoto lenses, the purpose of this invention is to provide an online lens temperature drift testing system and method based on reverse projection.

[0006] This application is achieved through the following technical solution: An online lens temperature drift testing system based on inverse projection includes: A closed, dry, constant-temperature environment system includes a closed metal cavity, which is provided with a glass measuring window and a cavity sealing cover. The closed metal cavity is filled with dry gas so that there is no water vapor inside the cavity and it is under normal pressure. The lens support is fixedly installed inside the sealed metal cavity to carry and support the lens under test; A TEC heating and cooling system, at least partially disposed within the sealed metal cavity, is used to provide an adjustable test temperature environment; The heat-conducting positioning fixture has its outer side in contact with the TEC heating and cooling system and its inner side in contact with the lens under test, and performs centering positioning and temperature conduction for the lens under test; A reverse projection MTF inspection system includes a reticle and a motor that drives the reticle to move linearly along the optical axis. The control module is electrically connected to the TEC heating and cooling system, the reverse projection MTF detection system, and the sealed dry constant temperature environment system, respectively. It is used to control the TEC heating and cooling system to adjust the temperature of the lens under test, and to control the motor to drive the reticle to move to scan the defocus curve. In this way, the back focus change of the lens under test can be calculated by finding the motor position corresponding to the optimal MTF state at different temperatures.

[0007] As described above, the closed-loop dry constant temperature environment system further includes a constant temperature water circulation device and an air drying device for filling the closed metal cavity with dry gas. A first cold water drain is pre-embedded in the inner wall of the closed metal cavity. The first cold water drain is connected to the constant temperature water circulation device through a pipe. The constant temperature water circulation device maintains the inner wall of the closed metal cavity at a set constant temperature. The inner wall of the closed metal cavity is provided with an Invar steel mounting plate.

[0008] In the testing system described above, the lens support is made of quartz glass and is mounted on the Invar steel mounting plate. The motor that drives the reticle movement in the reverse projection MTF detection system is also mounted on the Invar steel mounting plate.

[0009] As described above, the TEC heating and cooling system includes a controller, a cooling circulation system, a TEC cooling plate, a heat-conducting component located within the sealed metal cavity, and a second cold water drain. One side of the TEC cooling plate is attached to the heat-conducting component, and the other side is attached to the second cold water drain. The second cold water drain is connected to the cooling circulation system via a pipe. The heat-conducting positioning fixture has a ring-shaped structure. The outer ring of the heat-conducting positioning fixture contacts the heat-conducting component, and the inner ring contacts the lens under test, so as to press and wrap the lens under test for uniform heating or cooling.

[0010] As described above, the inverse projection MTF testing system further includes a swing arm motor, a camera swing arm connected to the output end of the swing arm motor, a testing camera mounted on the camera swing arm, and a light source. The light emitted by the light source passes through the reticle and projects a pattern from the image plane end of the lens under test to the space in front of the lens. The testing camera is located directly in front of the lens under test and is used to capture images of the lens under test through the glass measurement window on the sealed metal cavity. The camera swing arm drives the testing camera to swing to different angles to measure the temperature drift of the lens under test under different fields of view.

[0011] In the testing system described above, the motor is a high-precision linear motor or a lead screw stepper motor; the heat-conducting positioning fixture and the heat-conducting component are made of copper.

[0012] An online lens temperature drift testing method based on inverse projection, applied to the testing system described in any of the preceding claims, includes the following steps: Step S1: Place the lens to be tested on the lens support in the sealed metal cavity, install the heat-conducting positioning fixture on the lens to be tested, and cover the cavity with a sealing cover. Step S2: Fill the sealed metal cavity with dry gas; Step S3: Set the temperature to room temperature using the TEC heating and cooling system. After the temperature reaches equilibrium and the lens stress is released, control the motor of the reverse projection MTF detection system to move the reticle to scan the MTF peak position. Record the absolute position of the motor at the MTF peak as the back focal reference position at room temperature, and record the MTF peak as the room temperature MTF reference value. Step S4: The temperature is set to the target test temperature through the TEC heating and cooling system. After the temperature reaches equilibrium and the lens stress is released, the motor is controlled to drive the reticle to move and perform MTF peak position scanning to obtain the MTF peak value at the target test temperature and the corresponding absolute position of the motor. Step S5: Calculate the difference between the back focal reference position at room temperature and the absolute position of the motor corresponding to the MTF peak value at the target test temperature, and obtain the back focal change of the lens under test at the target test temperature; calculate the difference between the MTF reference value at room temperature and the MTF peak value at the target test temperature, and obtain the MTF change of the lens under test at the target test temperature.

[0013] In the test method described above, in step S5, the displacement of the reticle driven by the motor has a one-to-one conversion relationship with the change in back focal length of the lens under test.

[0014] As described above, in the testing method, the steps of scanning the MTF peak position in steps S3 and S4 include: The motor is controlled to move according to a preset range and step size; each time the motor moves, the detection camera is controlled to capture an image and calculate the MTF value at the current position; based on the various moving positions of the motor and the corresponding acquired MTF values, an MTF defocus parabola is fitted; based on the MTF defocus parabola, the MTF peak value and the absolute position of the motor corresponding to the MTF peak value are calculated.

[0015] As described above, in step S4, the target test temperature includes a high-temperature test temperature and a low-temperature test temperature. After obtaining the room temperature reference, the lens temperature inside the cavity is changed by the TEC heating and cooling system, thereby completing the online testing of back focal length change and MTF data under high and low temperature environments without removing the lens under test.

[0016] Compared with the prior art, this application has the following advantages: 1. This invention abandons the traditional vacuuming method. By filling the sealed metal cavity with dry gas, it not only ensures that the cavity does not frost at low temperatures, but also keeps the cavity at normal pressure. This avoids structural deformation of the airtight vehicle lens due to negative pressure, and the test results are more in line with actual application scenarios.

[0017] 2. This invention utilizes quartz glass, which has extremely low thermal conductivity and a low coefficient of thermal expansion, as a lens support component. The lens support component and the motor are simultaneously fixed on an Invar steel mounting plate equipped with a first cooling water drain for constant temperature. This physical material solution locks the absolute position of the lens relative to the motor, which not only ensures the testing accuracy but also completely eliminates the need for expensive air gap measuring instruments and reference glass found in foreign equipment, significantly reducing system costs.

[0018] 3. A circular thermally conductive positioning fixture made of copper was designed. Its inner ring tightly presses against and wraps the lens to be tested. Through heat conduction and radiation, it achieves uniform heating and cooling from all directions, effectively eliminating the temperature gradient problem caused by traditional bottom heating and significantly improving the measurement accuracy of telephoto lenses.

[0019] 4. The lens under test can be continuously measured online at room temperature, high temperature and low temperature in one go within the test bench. There is no need to move it back and forth. The difference in the position of the motor is directly equivalent to the change in back focus by 1:1. The test process is convenient and the data is highly reliable. [Attached Image Description] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below.

[0021] Figure 1 This is a front view of an embodiment of this application; Figure 2 This is a side view of an embodiment of this application; Figure 3This is a top view of an embodiment of this application; Figure 4 This is a schematic block diagram of the online testing system according to an embodiment of this application; Figure 5 This is a schematic diagram of the inverse projection MTF detection system in the embodiments of this application; Figure 6 This is a schematic diagram of the closed, dry, constant-temperature environment system in the embodiments of this application; Figure 7 This is a schematic block diagram of the TEC heating and cooling system in the embodiments of this application; Figure 8 This is a flowchart of the online testing method according to an embodiment of this application.

Detailed Implementation Methods

[0023] Please see Figures 1 to 8 An online lens temperature drift testing system based on inverse projection includes: A closed, dry, constant-temperature environment system 1 includes a closed metal cavity 11, the closed metal cavity 11 is provided with a glass measuring window 16 and a cavity sealing cover 17, and the closed metal cavity 11 is filled with dry gas so that there is no water vapor inside the cavity and it is under normal pressure. Lens support 2 is fixedly installed inside the sealed metal cavity 11 to carry and support the lens 3 to be tested. The TEC heating and cooling system 4, which is at least partially disposed within the sealed metal cavity 11, is used to provide an adjustable test temperature environment; The heat-conducting positioning fixture 5 has its outer side in contact with the TEC heating and cooling system 4 and its inner side in contact with the lens under test 3, and performs center positioning and temperature conduction for the lens under test 3; The reverse projection MTF detection system 6 includes a reticle 61 and a motor 62 that drives the reticle 61 to move linearly along the optical axis. The control module 7 is electrically connected to the TEC heating and cooling system 4, the reverse projection MTF detection system 6, and the sealed dry constant temperature environment system 1, respectively. It is used to control the TEC heating and cooling system 4 to adjust the temperature of the lens under test 3, and to control the motor 62 to drive the reticle 61 to move to scan the defocus curve, thereby calculating the back focus change of the lens under test 3 by finding the motor position corresponding to the optimal MTF state at different temperatures.

[0024] In this embodiment, the sealed, dry, and constant-temperature environment system 1 includes a sealed metal cavity 11. The sealed metal cavity 11 is provided with a glass measurement window 16 to facilitate the transmission of optical detection signals, and a cavity sealing cover 17 for easy handling of the lens 3 under test. During testing, dry gas is introduced into the sealed metal cavity 11. The dry gas can be high-purity nitrogen or air that has undergone deep dehumidification and drying treatment, ensuring that the internal environment of the cavity is essentially free of water vapor and maintained at normal pressure. This non-vacuum, normal-pressure drying design effectively prevents lens deformation or structural changes in vehicle-mounted lenses with waterproof and airtight designs under negative pressure environments. It also effectively prevents frost formation under low-temperature testing conditions, making the testing process smoother. The environment is more closely aligned with the actual working conditions of the lens; the lens support 2 is fixedly installed inside the sealed metal cavity 11, providing a stable bearing and physical support benchmark for the lens under test 3; at least some of the heating or cooling heat exchange elements of the TEC heating and cooling system 4 are located inside the sealed metal cavity 11, providing a continuously adjustable test temperature environment from high to low temperature for the lens under test 3; to improve the uniformity of temperature conduction, this solution includes a heat-conducting positioning fixture 5, whose outer surface is attached to the hot and cold output ends of the TEC heating and cooling system 4, while its inner surface contacts the outer wall of the lens under test 3. This achieves physical centering of the lens under test 3, while uniformly distributing cold or heat through contact conduction and thermal radiation. The temperature gradient is transferred to the entire lens under test 3, reducing the radial and axial temperature gradients of the lens. The reverse projection MTF detection system 6 includes a reticle 61 and a motor 62 connected to it. The motor 62 can be a high-precision linear motor, a lead screw stepper motor, or other drive mechanism with precise linear displacement output, which can drive the reticle 61 to move linearly in a stepping manner along the optical axis. The control module 7 can be an industrial control computer, a PLC controller, or a customized single-chip microcomputer system, etc., and is electrically connected and communicates with the TEC heating and cooling system 4, the reverse projection MTF detection system 6, and the sealed dry constant temperature environment system 1, respectively. During actual testing, the control module 7 issues commands to control the TEC heating and cooling system 4 to adjust to Once the target test temperature is set and the temperature inside the cavity stabilizes, the control module 7 instructs the motor 62 to move the reticle 61 back and forth within the set displacement range. This, in conjunction with the optical imaging component, sequentially acquires image data from different positions to scan and fit the MTF defocus curve. Subsequently, the mechanical coordinate position of the motor 62 corresponding to the optimal MTF state (i.e., peak value) is found under different temperature environments. Since the overall system structure remains relatively stable, the back focus change of the lens under test 3 at the corresponding temperature can be calculated by directly comparing the relative difference between the optimal coordinate positions of the motor 62 at different temperatures. This design enables online continuous testing without moving the lens under test 3, which helps to improve the convenience of the temperature drift test process and the accuracy of the measurement data.

[0025] Furthermore, as a preferred embodiment of this solution and not a limitation thereof, the sealed drying constant temperature environment system 1 further includes a constant temperature water circulation device 12 and an air drying device 13 for filling the sealed metal cavity 11 with drying gas. A first cold water drain 14 is pre-embedded in the inner wall of the sealed metal cavity 11. The first cold water drain 14 is connected to the constant temperature water circulation device 12 through a pipe. The constant temperature water circulation device 12 maintains the inner wall of the sealed metal cavity 11 at a set constant temperature. The inner wall of the sealed metal cavity 11 is provided with an Invar steel mounting plate 15.

[0026] In this embodiment, a first cold water drain 14 is pre-embedded in the inner wall of the sealed metal cavity 11. The first cold water drain 14 is connected to the constant temperature water circulation device 12 through a corresponding fluid pipe, and an Invar steel mounting plate 15 is fixedly installed on the inner wall of the sealed metal cavity 11. The constant temperature water circulation device 12 drives the circulating liquid. In practical applications, the circulating liquid can be water, or it can be replaced with other heat exchange fluid media such as low-volatility oil or special refrigerant, depending on the specific working conditions and design requirements. It continuously circulates in the first cold water drain 14. Through heat exchange, the constant temperature water circulation device 12 maintains the inner wall of the sealed metal cavity 11 at a set constant temperature range for a long time. At the same time, the air drying device 13 introduces dry gas into the sealed metal cavity 11 to replace and discharge the air that originally contained moisture. The beneficial effects of the above-mentioned structural combination are as follows: Firstly, the continuous or intermittent filling of dry gas can significantly reduce the ambient humidity inside the cavity, preventing frost formation on the structural components and the surface of the lens under test during low-temperature testing, thus ensuring the smooth operation of the optical testing path; secondly, the constant-temperature water circulation design can effectively absorb and remove the residual heat dissipated by temperature conduction inside the cavity, combined with the very low coefficient of thermal expansion of the Invar steel mounting plate 15 (its coefficient of thermal expansion is approximately 1.0 × 10⁻⁶). -6 / ℃), which allows the Invar steel mounting plate 15 to maintain good dimensional and morphological stability during long-term testing, thus providing a structural reference for other test components mounted on it that is not easily displaced by fluctuations in ambient temperature, which helps to improve the reliability and accuracy of back coke measurement data. In addition, in other feasible alternative embodiments, the air drying device 13 can also achieve the controlled injection of drying gas through a pipeline structure with an external high-purity nitrogen cylinder, a pressure reducing valve and a flow meter, which can also achieve the technical purpose of preventing frost formation.

[0027] Furthermore, as a preferred embodiment of this solution and not a limitation, the lens support 2 is made of quartz glass and is mounted on the Invar steel mounting plate 15, and the motor 62 that drives the reticle 61 of the reverse projection MTF detection system 6 is mounted on the Invar steel mounting plate 15.

[0028] In this embodiment, the motor 62 in the reverse projection MTF detection system 6, which drives the reticle 61 to perform scanning motion, is also fixedly mounted on the same Invar steel mounting plate 15. Regarding its working principle, the quartz glass material itself possesses excellent heat insulation properties and a temperature as low as approximately 0.5 × 10⁻⁶. -6 The coefficient of thermal expansion is approximately 1.0 × 10⁻⁶ °C, while the coefficient of thermal expansion of the Invar steel mounting plate 15 is also controlled at approximately 1.0 × 10⁻⁶ °C. -6 At a temperature of approximately ℃, when the TEC heating and cooling system adjusts the high and low temperature environment of the lens under test, the quartz glass can effectively block most of the heat or cold energy from being conducted to the rear cavity wall. The small amount of heat energy transferred can be promptly carried away by the constant temperature water circulation system on the inner wall of the cavity, making the thickness of the quartz glass itself and the shape of the Invar steel mounting plate 15 less prone to significant dimensional deformation under temperature fluctuations. Since the lens support 2 and the motor 62 are both mounted on the same Invar steel mounting plate 15 with a common reference, this common reference and low expansion combination design can ensure that the relative mechanical position relationship between the mounting position of the motor 62 and the bearing reference surface of the lens support 2 remains basically stable when the motor is not moving. Its beneficial effect is that this design can achieve the desired effect without the need for expensive external interval measuring instruments. It is worth mentioning that by utilizing the low expansion and low thermal conductivity of the material, a relatively static physical reference benchmark is constructed inside the test chamber, which is unaffected by the temperature changes of the test piece. This allows the displacement difference obtained by the motor 62 driving the reticle 61 to scan to more accurately reflect the back focal offset of the lens under test, thereby improving the data accuracy of the temperature drift test and reasonably controlling the manufacturing cost of the equipment. In other feasible alternative embodiments, the material of the lens support 2 is not limited to quartz glass. Depending on the actual processing conditions and test accuracy requirements, it can also be replaced with other heat-insulating materials with similar micro-expansion or near-zero expansion characteristics, such as microcrystalline glass and low-expansion ceramics, which can also achieve the technical purpose of maintaining a relatively constant support position, providing a richer engineering selection space for the implementation of the present invention.

[0029] Furthermore, as a preferred embodiment of this solution and not a limitation thereof, the TEC heating and cooling system 4 includes a controller 41, a cooling circulation system 42, a TEC cooling plate 43, a heat-conducting component 44 located within the sealed metal cavity 11, and a second cold water drain 45. One side of the TEC cooling plate 43 is attached to the heat-conducting component 44, and the other side is attached to the second cold water drain 45. The second cold water drain 45 is connected to the cooling circulation system 42 via a pipe. The heat-conducting positioning fixture 5 has a ring-shaped structure. The outer ring of the heat-conducting positioning fixture 5 contacts the heat-conducting component 44, and the inner ring contacts the lens 3 under test, so as to press and wrap the lens 3 under test for uniform heating or cooling.

[0030] In this embodiment, the controller 41 outputs a control current to the TEC cooling chip 43 to achieve heating or cooling functions. When the TEC cooling chip 43 cools or heats the heat-conducting component 44, the excess heat or cold generated on the other side is dissipated by the second cold water drain 45 and the circulating liquid flowing in it into the cooling circulation system 42, thereby maintaining the working efficiency of the TEC cooling chip 43 and the temperature environment stability of the heat-conducting component 44. In order to efficiently transfer the temperature of the heat-conducting component 44 to the test object, in this embodiment, the heat-conducting positioning fixture 5 is designed as a ring structure. The outer ring of the heat-conducting positioning fixture 5 is in close contact with the heat-conducting component 44 for heat exchange, and its inner ring is in contact with the lens under test 3, thereby pressing and wrapping the lens under test 3 to uniformly heat or cool it. The beneficial effect of the fully enclosed ring-shaped heat conduction design is that it effectively improves the uneven heating of the lens that is easily caused by the traditional single-sided bottom support heating scheme through large-area heat conduction and heat radiation, reduces the temperature gradient inside the lens under test 3, thereby improving the uniformity of temperature control and the measurement accuracy of test samples such as telephoto lenses; in other feasible alternative embodiments, in addition to using copper as the preferred high thermal conductivity material for the heat conduction component 44 and the heat conduction positioning fixture 5, it can also be replaced with other materials with excellent thermal conductivity, such as high thermal conductivity aluminum alloy and graphene thermal conductive composite material, depending on the actual processing cost or specific needs. In addition to conventional cooling water, the circulating liquid filled in the cooling circulation system 42 can also be low-volatility heat conduction oil or special antifreeze.

[0031] Furthermore, as a preferred embodiment of this solution and not a limitation thereof, the reverse projection MTF detection system 6 also includes a swing arm motor 66, a camera swing arm 63 connected to the output end of the swing arm motor 66, a detection camera 64 mounted on the camera swing arm 63, and a light source 65. The light emitted by the light source 65 passes through the reticle 61 and projects a pattern from the image plane end of the lens under test 3 to the space in front of the lens. The detection camera 64 is located directly in front of the lens under test 3 and is used to capture images of the lens under test 3 through the glass measurement window 16 on the sealed metal cavity 11. The camera swing arm 63 drives the detection camera 64 to swing to different angles to measure the temperature drift of the lens under test 3 under different fields of view.

[0032] In this embodiment, the light beam emitted by the light source 65 first passes through the reticle 61, typically projecting specific patterns such as cross slits in practical applications. Then, the light enters from the image plane of the lens under test 3 and projects the corresponding test pattern backwards from the inside out into the space in front of the lens. Simultaneously, the detection camera 64 is positioned directly in front of the lens under test 3, and can clearly capture the optical image refracted and transmitted through the glass measurement window 16 on the sealed metal cavity 11. During multi-field testing, the system controls the swing arm motor 66 to drive the camera swing arm 63, causing the detection camera 64 to swing around the lens under test to different angular positions. The advantage of this design, based on reverse projection combined with a swing arm camera, is that it eliminates the need for complex image acquisition arrangements within the confined, sealed, temperature-controlled cavity. The probe can be integrated without moving the lens 3 under test itself, enabling comprehensive online measurement of temperature drift at the center and edges of the lens 3 under different fields of view in a non-contact manner. This effectively expands the detection dimensions and data coverage of the equipment, and helps to more objectively evaluate the optical performance of the camera module. In other feasible alternative embodiments, the transmission mechanism of the swing arm motor 66 can be combined with a high-precision servo motor and a harmonic reducer or worm gear assembly to further improve the stability and positioning accuracy of the camera's angle hovering. Furthermore, the glass measurement window 16 can be designed as an arc-shaped surface structure with appropriate curvature or an ultra-wide-space plane structure according to the motion trajectory envelope of the camera swing, thereby ensuring that the camera 64 can obtain clear optical images with no border obstruction and low distortion through the window at different swing test angles, providing reliable engineering assurance for the multi-field detection function of the testing system.

[0033] Furthermore, as a preferred embodiment of this solution and not a limitation, the motor 62 is a high-precision linear motor or a lead screw stepper motor; the heat-conducting positioning fixture 5 and the heat-conducting component 44 are made of copper.

[0034] An online lens temperature drift testing method based on inverse projection, applied to the testing system described in any of the preceding claims, includes the following steps: Step S1: Place the lens to be tested 3 on the lens support 2 inside the sealed metal cavity 11, install the heat-conducting positioning fixture 5 on the lens to be tested 3, and cover the cavity sealing cover plate 17. Step S2: Fill the sealed metal cavity 11 with dry gas; Step S3: The temperature is set to room temperature by the TEC heating and cooling system 4. After the temperature reaches equilibrium and the lens stress is released, the motor 62 of the reverse projection MTF detection system 6 is controlled to move the reticle 61 to scan the MTF peak position. The absolute position of the motor at the MTF peak is recorded as the back focal reference position at room temperature, and the MTF peak value is recorded as the room temperature MTF reference value. Step S4: The temperature is set to the target test temperature through the TEC heating and cooling system 4. After the temperature reaches equilibrium and the lens stress is released, the motor 62 is controlled to drive the reticle 61 to move and perform MTF peak position scanning to obtain the MTF peak value at the target test temperature and the corresponding absolute position of the motor 62. Step S5: Calculate the difference between the back focal reference position at room temperature and the absolute position of the motor corresponding to the MTF peak value at the target test temperature, and obtain the back focal change of the lens under test 3 at the target test temperature; calculate the difference between the MTF reference value at room temperature and the MTF peak value at the target test temperature, and obtain the MTF change of the lens under test 3 at the target test temperature.

[0035] In this embodiment, the method first performs step S1, where the operator securely places the lens under test 3 onto the lens support 2 (i.e., the support reference) within the sealed metal cavity 11, then installs the thermally conductive positioning fixture 5 onto the lens under test 3, and covers it with the cavity sealing cover 17, thereby creating a relatively closed and initially stable test environment in physical space for subsequent testing; next, step S2 is performed, where dry gas is injected into the sealed metal cavity 11 through a gas path device. The beneficial effect of this step is that it can effectively replace the moisture originally contained inside the cavity, so that the test environment is always maintained at normal pressure and dry state, thereby effectively preventing the formation of deposits on the surface of the lens under test 3 and the internal components of the cavity during subsequent low-temperature environment testing. The frost phenomenon ensures the normal transmission and acquisition of optical signals; then, in step S3 of the reference acquisition stage, the internal temperature is set to room temperature, such as 25°C under normal standards, through the TEC heating and cooling system 4. After the temperature reaches thermal equilibrium and a period of time is waited for the thermal and mechanical stress of the lens under test 3 to be fully released, the control module issues a command to control the motor 62 in the reverse projection MTF detection system 6 to drive the reticle 61 to move along the optical axis to perform MTF peak position scanning; at this time, the system will record and store the absolute mechanical position of the motor 62 when the MTF peak is detected as the back focal reference position at room temperature, and at the same time record the MTF peak as the room temperature MTF reference value, as the reference data for subsequent comparison; after completing the room temperature base... After calibration, step S4 is executed. The ambient temperature is adjusted again by the TEC heating and cooling system 4 and set to the target test temperature, such as a high-temperature condition or a low-temperature condition. Similarly, after the temperature reaches equilibrium and the lens stress is released and stabilized, the motor 62 is controlled again to move the reticle 61 and perform the same MTF peak position scan to obtain the MTF peak value at the target test temperature and the corresponding current absolute position of the motor 62. Finally, step S5 is executed. Since the relative mechanical distance between the lens bearing surface and the motor base of the entire system remains stable during the temperature change process due to the protection of the low-expansion material, the electrical distance between the back focal reference position at room temperature and the MTF peak value at the target test temperature is directly calculated. The difference in absolute position of the machine can be used to obtain the back focal length change of the lens under test 3 at the target test temperature. At the same time, the difference between the MTF reference value at room temperature and the MTF peak value at the target test temperature can be calculated to quantify the MTF change of the lens under test 3 at the target test temperature. The beneficial effects of the above test method are mainly reflected in the following aspects: it makes full use of the advantage of the relatively constant hardware spatial reference, and transforms the high and low temperature performance changes of the lens under test into the displacement changes of the motor in a unified coordinate system. Not only is the test logic simple and efficient, but it also avoids the rapid drop in shell temperature and secondary clamping and positioning errors caused by moving the lens under test back and forth between the high temperature oven and professional instruments in traditional tests, which significantly improves the authenticity and reliability of temperature drift test data.In other feasible alternative implementations, during the target temperature test in step S4, the control system can perform multi-segment automatic temperature rise and fall scanning tests according to a preset continuous temperature gradient, for example, with each 10°C serving as a data acquisition node. This allows R&D analysts to automatically plot a continuous temperature drift curve of the lens under test across the entire wide temperature range, further expanding the application depth of this online testing method in the field of camera module temperature drift compensation design.

[0036] Furthermore, as a preferred embodiment of this solution and not a limitation, in step S5, the displacement of the reticle 61 driven by the motor 62 has a one-to-one conversion relationship with the back focal length change of the lens 3 under test.

[0037] In this embodiment, the establishment of this one-to-one correspondence benefits from the low thermal expansion physical reference jointly constructed by the Invar steel material of the inner wall of the aforementioned sealed metal cavity and the quartz glass material of the lens support. Under this structural combination, the structural distance between the reference surface supporting the lens 3 under test and the mounting surface of the fixed motor 62 maintains high physical stability in the variable temperature test environment. Therefore, when the test temperature changes and causes temperature drift in the internal optical system of the lens 3 under test, the spatial offset of its focal position can be directly and realistically reflected in the mechanical displacement required by the reticle 61 to find the new MTF peak. That is, the physical travel distance of the motor 62 to find the clearest imaging point is directly equivalent to the optical offset distance of the focal plane of the lens 3 under test. The beneficial effect of this one-to-one direct conversion design is that it eliminates the complex optical magnification conversion formula and additional mechanical error compensation calculation at the software algorithm level. It not only simplifies the data processing logic of the control module and improves the efficiency of software operation feedback, but also effectively avoids the data accumulation error that may be caused by indirect calculation in multiple links, making the back focal offset result obtained by the test more intuitive and reliable.

[0038] Furthermore, as a preferred embodiment of this solution and not a limitation, the step of scanning the MTF peak position in steps S3 and S4 includes: The motor 62 is controlled to move according to a preset moving range and step size; each time the motor moves, the detection camera 64 is controlled to capture an image and calculate the MTF value at the current position; based on the various moving positions of the motor 62 and the corresponding acquired MTF values, an MTF defocus parabola is fitted; based on the MTF defocus parabola, the MTF peak value and the absolute position of the motor corresponding to the MTF peak value are calculated.

[0039] In this embodiment, the control module first issues a command to control the motor 62 to move step by step along the optical axis according to the movement range preset by the system and a small step amount. During this dynamic scanning process, each time the motor 62 completes a step movement, the control module synchronously triggers the detection camera 64 to capture the target image through the lens under test, and calculates the MTF value at the current physical position in real time through the internal image analysis algorithm. As the scanning action progresses, the system collects a set of discrete coordinates of the movement position of the motor 62 and the corresponding MTF value. Based on this set of corresponding data, the data processing unit uses a mathematical fitting algorithm to generate an MTF defocus parabola that reflects the trend of image quality change before and after the focus. Subsequently, the system accurately analyzes the MTF peak value represented by the vertex of the parabola according to the mathematical model of the MTF defocus parabola, and calculates the absolute position of the motor corresponding to the MTF peak value. This peak-finding design, which combines multi-point step scanning with parabolic fitting, avoids the drawbacks of relying solely on single-acquisition comparisons, which are easily affected by local image noise or slight mechanical jitter. By smoothing the global curve, it effectively filters out abnormal jump data during the measurement process, improves the accuracy of the focal point positioning coordinates and the consistency of repeated measurements, and makes the final measured back focal offset data more objective and reliable.

[0040] Furthermore, as a preferred embodiment of this solution and not a limitation, in step S4, the target test temperature includes a high-temperature test temperature and a low-temperature test temperature. After obtaining the room temperature reference, the lens temperature inside the cavity is changed by the TEC heating and cooling system 4, thereby completing the online testing of back focal length change and MTF data under high and low temperature environments without removing the lens 3 under test.

[0041] In this embodiment, after the system successfully acquires the ambient temperature reference data in step S3, the control module directly issues a new temperature adjustment command to the TEC heating and cooling system 4. The TEC heating and cooling system 4 then changes the local test environment temperature within the sealed cavity through its cooling element and associated heat-conducting components, and uniformly transfers heat or cold to the lens under test 3 through a fully enclosed fixture, allowing it to stably reach the set high or low temperature state. The beneficial effect of this test process design is that the entire temperature change and optical scanning process is carried out continuously in a sealed space protected by low-expansion materials and with a relatively constant physical reference. During this period, the tester does not need to open the cavity cover, thus enabling one-stop online acquisition and testing of back focal length change and MTF data under high and low temperature environments without removing the lens under test 3. This design not only simplifies the cumbersome operation of temperature drift testing and avoids many interference factors such as rapid temperature loss, condensation and frost, and secondary clamping and positioning errors caused by moving the lens back and forth between the high-temperature oven and the room temperature tester in traditional testing methods, but also effectively improves the detection efficiency and data authenticity of the camera module in a wide temperature range.

[0042] The working principle of this embodiment is as follows: During the testing process, the lens under test is first placed in a sealed metal cavity filled with dry gas to prevent low-temperature frost formation and maintain normal pressure within the cavity. Simultaneously, an Invar steel mounting plate with a pre-embedded constant-temperature cooling water drain and a quartz glass lens support are used to construct a low-expansion physical reference standard that is not easily affected by localized temperature variations. Subsequently, the lens under test is uniformly heated and cooled using a TEC heating and cooling system in conjunction with a fully enclosed annular thermally conductive positioning fixture. Once the lens reaches thermal stress equilibrium at the set target temperature, the control module drives the motor of the reverse projection MTF detection system to perform a step-scan along the optical axis. Combined with image data acquired by the detection camera, the MTF defocus parabola is fitted in real time to locate the MTF peak coordinates at that temperature. Based on this relatively constant physical reference standard, the system can directly calculate the difference between the absolute coordinates of the motor corresponding to the MTF peak at the normal temperature reference and the target test temperature without removing the lens or using external ranging instruments. This allows for a one-to-one acquisition of the back focus change and MTF change data of the lens under test under different ambient temperatures, thus achieving one-stop online high and low temperature drift testing.

[0043] The above are implementation methods provided in conjunction with specific content, and it is not intended that the specific implementation of this application is limited to these descriptions.

Claims

1. An online lens temperature drift testing system based on inverse projection, characterized in that, include: A closed, dry, constant temperature environment system (1) includes a closed metal cavity (11), the closed metal cavity (11) is provided with a glass measuring window (16) and a cavity sealing cover (17), the closed metal cavity (11) is filled with dry gas so that there is no water vapor inside the cavity and it is under normal pressure. The lens support (2) is fixedly installed inside the sealed metal cavity (11) and is used to carry and support the lens (3) to be tested. The TEC heating and cooling system (4), which is at least partially disposed within the sealed metal cavity (11), is used to provide an adjustable test temperature environment; The heat-conducting positioning fixture (5) has its outer side in contact with the TEC heating and cooling system (4) and its inner side in contact with the lens to be tested (3), and performs center positioning and temperature conduction on the lens to be tested (3); The reverse projection MTF detection system (6) includes a reticle (61) and a motor (62) that drives the reticle (61) to move linearly along the optical axis. The control module (7) is electrically connected to the TEC heating and cooling system (4), the reverse projection MTF detection system (6), and the sealed dry constant temperature environment system (1), respectively. It is used to control the TEC heating and cooling system (4) to adjust the temperature of the lens under test (3), and to control the motor (62) to drive the reticle (61) to move to scan the defocus curve, thereby calculating the back focus change of the lens under test (3) by finding the motor position corresponding to the optimal MTF state at different temperatures.

2. The testing system according to claim 1, characterized in that, The sealed dry constant temperature environment system (1) further includes a constant temperature water circulation device (12) and an air drying device (13) for filling the sealed metal cavity (11) with dry gas. A first cold water drain (14) is pre-embedded in the inner wall of the sealed metal cavity (11). The first cold water drain (14) is connected to the constant temperature water circulation device (12) through a pipe. The constant temperature water circulation device (12) maintains the inner wall of the sealed metal cavity (11) at a set constant temperature. The inner wall of the sealed metal cavity (11) is provided with an Invar steel mounting plate (15).

3. The testing system according to claim 2, characterized in that, The lens support (2) is made of quartz glass and is mounted on the Invar steel mounting plate (15). The motor (62) that drives the reticle (61) of the reverse projection MTF detection system (6) is mounted on the Invar steel mounting plate (15).

4. The testing system according to claim 2, characterized in that, The TEC heating and cooling system (4) includes a controller (41), a cooling circulation system (42), a TEC cooling chip (43), a heat-conducting component (44) located in the sealed metal cavity (11), and a second cold water drain (45). One side of the TEC cooling chip (43) is attached to the heat-conducting component (44), and the other side is attached to the second cold water drain (45). The second cold water drain (45) is connected to the cooling circulation system (42) through a pipe. The heat-conducting positioning fixture (5) has a ring-shaped structure. The outer ring of the heat-conducting positioning fixture (5) contacts the heat-conducting component (44), and the inner ring contacts the lens under test (3) to press and wrap the lens under test (3) for uniform heating or cooling.

5. The testing system according to claim 1, characterized in that, The reverse projection MTF detection system (6) also includes a swing arm motor (66), a camera swing arm (63) connected to the output end of the swing arm motor (66), a detection camera (64) mounted on the camera swing arm (63), and a light source (65). The light emitted by the light source (65) passes through the reticle (61) and projects a pattern from the image plane end of the lens under test (3) to the space in front of the lens. The detection camera (64) is located directly in front of the lens under test (3) and is used to capture images of the lens under test (3) through the glass measurement window (16) on the sealed metal cavity (11). The camera swing arm (63) drives the detection camera (64) to swing to different angles to measure the temperature drift of the lens under test (3) under different fields of view.

6. The testing system according to claim 4, characterized in that, The motor (62) is a high-precision linear motor or a lead screw stepper motor; the heat-conducting positioning fixture (5) and the heat-conducting component (44) are made of copper.

7. A method for online testing of lens temperature drift based on inverse projection, characterized in that, Applied to the test system according to any one of claims 1-6, the method includes the following steps: Step S1: Place the lens to be tested (3) on the lens support (2) inside the sealed metal cavity (11), install the heat-conducting positioning fixture (5) on the lens to be tested (3), and cover the cavity sealing cover (17). Step S2: Fill the sealed metal cavity (11) with dry gas; Step S3: The temperature is set to room temperature by the TEC heating and cooling system (4). After the temperature reaches equilibrium and the lens stress is released, the motor (62) of the reverse projection MTF detection system (6) is controlled to drive the reticle (61) to move and scan the MTF peak position. The absolute position of the motor at the MTF peak is recorded as the back focal reference position at room temperature, and the MTF peak is recorded as the room temperature MTF reference value. Step S4: The temperature is set to the target test temperature through the TEC heating and cooling system (4). After the temperature reaches equilibrium and the lens stress is released, the motor (62) is controlled to drive the reticle (61) to move and scan the MTF peak position to obtain the MTF peak at the target test temperature and the corresponding absolute position of the motor (62). Step S5: Calculate the difference between the back focal reference position at room temperature and the absolute position of the motor corresponding to the MTF peak value at the target test temperature, and obtain the back focal change of the lens under test (3) at the target test temperature; calculate the difference between the MTF reference value at room temperature and the MTF peak value at the target test temperature, and obtain the MTF change of the lens under test (3) at the target test temperature.

8. The test method according to claim 7, characterized in that, In step S5, the displacement of the reticle (61) driven by the motor (62) has a one-to-one conversion relationship with the back focal length change of the lens (3) under test.

9. The test method according to claim 7, characterized in that, In steps S3 and S4, the steps of scanning the MTF peak position include: The motor (62) is controlled to move according to a preset moving range and step size; each time the motor moves, the detection camera (64) is controlled to capture an image and calculate the MTF value at the current position; based on the various moving positions of the motor (62) and the corresponding acquired MTF values, an MTF defocus parabola is fitted; based on the MTF defocus parabola, the MTF peak value and the absolute position of the motor corresponding to the MTF peak value are calculated.

10. The test method according to claim 7, characterized in that, In step S4, the target test temperature includes a high temperature test temperature and a low temperature test temperature. After the room temperature reference is obtained, the lens temperature inside the cavity is changed by the TEC heating and cooling system (4), so that the back focal length change and MTF data under high temperature and low temperature environments can be tested online without removing the lens to be tested (3).

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