Transmission-type lens eccentricity and focal length detection device based on differential confocal response

Abstract

The invention discloses a transmission-type lens eccentricity and focal length detection device based on differential confocal response. The device comprises a double-laser light source, a collimating lens group, a detected lens group, an air suspension rotary lifting platform, a spectroscope, a first photoelectric detector and a differential confocal light path, the distance between the on-axis light source and the off-axis light source is a fixed value, and the on-axis light source and the off-axis light source are located on the same plane; the on-axis light source is positioned on a central axis of the collimating lens group, the air-suspending rotary lifting platform, the spectroscope and the first photoelectric detector; a tested lens group is arranged on the air-suspending rotary lifting platform, and the air-suspending rotary lifting platform enables the tested lens group to rotate around a central shaft, lift along the central shaft and move horizontally; light beams of the double-laser light source are divided into two paths through the spectroscope, one path reaches the first photoelectric detector, and the other path reaches the differential confocal light path so as to draw a differential response curve. According to the invention, the focal length and eccentricity of the lens / lens are tested by using double laser light sources and a transmission-type differential confocal light path.

Description

Technical Field

[0001] The invention belongs to the technical field of optical detection, and in particular relates to a transmission type lens eccentricity and focal length detection device based on differential confocal response. Background Art

[0002] The most important parameters in the lens production and manufacturing process are the radius of curvature, focal length, eccentricity and other parameters of a single lens surface. These parameters are usually measured using a reflective detection device to measure a single surface. However, in the assembly process of the lens group, more attention is paid to the coordination between the lenses and the final eccentricity and focal length of the entire lens group rather than the parameters of a single optical surface. In order to check whether the eccentricity and focal length of the lens group meet the corresponding acceptance standards, the entire lens group needs to be tested, generally using a transmission test device.

[0003] Common focal length and eccentricity test devices usually use the clarity method to focus, that is, the "clearest" conjugate image of the graticule is identified by the human eye or algorithm. This method is affected by individual factors, environmental interference, and detector sensitivity, and the measurement error is large, which restricts the accuracy of eccentricity and focal length measurement. Therefore, it is necessary to find a more accurate way to identify the "clearest" point to avoid interference from individual factors and detectors and improve the accuracy and repeatability of the test. Laser differential confocal technology uses a pair of photoelectric detectors near the focus to record the relationship between the change in light intensity signal and position, and accurately locate the focus. It has high measurement accuracy, good repeatability, and strong anti-interference ability. Summary of the invention

[0004] The object of the present invention is to provide a transmission type lens eccentricity and focal length detection device based on differential confocal response, so as to solve the problem of large errors in focal length and eccentricity measurement according to the definition legal focus.

[0005] The technical solution of the present invention is as follows:

[0006] In a first aspect, the present invention provides a transmissive lens eccentricity and focal length detection device based on differential confocal response, the device comprising a dual laser light source, a collimating lens group, a lens group to be tested, an air-suspended rotary lifting platform, a beam splitter, a first photodetector and a differential confocal optical path;

[0007] The dual laser light source includes an on-axis light source and an off-axis light source with a constant distance from the on-axis light source, and the on-axis light source and the off-axis light source are on the same plane; the on-axis light source is located on the central axis of the collimating lens group, the air-suspended rotary lifting platform, the spectroscope and the first photodetector; the lens group to be tested is placed on the air-suspended rotary lifting platform, and the air-suspended rotary lifting platform enables the lens group to be tested to rotate around the central axis, rise and fall along the central axis, and move horizontally; the light beams of the dual laser light source are divided into two paths by the spectroscope, one path goes to the first photodetector, and the other path goes to the differential confocal optical path to draw a differential response curve;

[0008] During the test, the on-axis light source is turned on first, and the light beam passes through the collimating lens group, the lens group to be tested and the beam splitter to reach the first photodetector and the differential confocal optical path;

[0009] The air suspension rotary lifting platform moves up and down along the central axis, so that the lens group under test moves up and down along the central axis. The difference between the intensity signals received by the two detectors in the differential confocal optical path and the amount of movement of the air suspension rotary lifting platform are used to draw a differential response curve. The curve passes through the zero point, indicating that the focal plane of the lens group under test coincides with the light sensitive surface of the first photodetector at this time.

[0010] The air-suspended rotary lifting platform rotates around the central axis to make the lens group under test rotate around the central axis; if a circular track appears on the first photoelectric detector, the eccentricity of the lens group under test is calculated according to the radius of the circular track;

[0011] The air-suspended rotary lifting platform moves horizontally until the laser spot of the on-axis light source on the first photodetector no longer moves with the rotation of the lens group under test; the off-axis light source is turned on, the distance between the on-axis light source and the image point of the off-axis light source on the first photodetector is obtained, and the focal length of the lens group under test is calculated based on the distance between the on-axis light source and the off-axis light source and the distance between their image points.

[0012] In the above scheme, the differential confocal optical path includes a 1:1 beam splitter, a pre-focus pinhole, a third photodetector, a post-focus pinhole and a second photodetector;

[0013] The light beam to the differential confocal optical path is split into two paths again by a 1:1 beam splitter, one path passes through the pre-focus pinhole to the third photodetector, and the other path passes through the post-focus pinhole to the second photodetector. The defocus amounts of the second photodetector and the third photodetector are +L and -L, respectively.

[0014] In the above solution, the intensity signals received by the second photodetector and the third photodetector are subtracted to obtain the difference in intensity signals.

[0015] In the above scheme, the device also includes a control system;

[0016] The control system is used to control the movement of the air suspension rotary lifting platform, receive signals from the first photoelectric detector, the second photoelectric detector and the third photoelectric detector, and analyze and calculate the eccentricity and focal length of the measured lens group.

[0017] In the above scheme, the control system is also used to control the opening and closing of the on-axis light source and the off-axis light source.

[0018] In the above scheme, the on-axis light source and the off-axis light source are two identical lasers.

[0019] In the above scheme, the calculation of the eccentricity of the lens group under test includes:

[0020]

[0021] Where, χ is the eccentricity of the lens group under test, r is the radius of the circular trajectory,; 12 is the distance between the image points of the on-axis light source and the off-axis light source on the first photodetector, f o is the focal length of the collimating lens group; is the distance between the on-axis light source and the off-axis light source.

[0022] In the above scheme, the focal length of the lens group under test is calculated, including:

[0023]

[0024] Where, f is the focal length of the lens group being tested, l 12 is the distance between the image points of the on-axis light source and the off-axis light source on the first photodetector, f o is the focal length of the collimating lens group, and l is the distance between the on-axis light source and the off-axis light source.

[0025] In a second aspect, the present invention provides a method for using the above-mentioned transmissive lens eccentricity and focal length detection device based on differential confocal response, comprising the following steps:

[0026] During the test, the on-axis light source is turned on first, and the light beam passes through the collimating lens group, the lens group to be tested and the beam splitter to reach the first photodetector and the differential confocal optical path;

[0027] The air suspension rotary lifting platform moves up and down along the central axis, so that the lens group under test moves up and down along the central axis. The difference between the intensity signals received by the two detectors in the differential confocal optical path and the amount of movement of the air suspension rotary lifting platform are used to draw a differential response curve. The curve passes through the zero point, indicating that the focal plane of the lens group under test coincides with the light sensitive surface of the first photodetector at this time.

[0028] The air-suspended rotary lifting platform rotates around the central axis to make the lens group under test rotate around the central axis; if a circular track appears on the first photoelectric detector, the eccentricity of the lens group under test is calculated according to the radius of the circular track;

[0029] The air-suspended rotary lifting platform moves horizontally until the laser spot of the on-axis light source on the first photodetector no longer moves with the rotation of the lens group under test; the off-axis light source is turned on, the distance between the on-axis light source and the image point of the off-axis light source on the first photodetector is obtained, and the focal length of the lens group under test is calculated based on the distance between the on-axis light source and the off-axis light source and the distance between their image points.

[0030] In the above scheme, the calculation of the eccentricity of the lens group under test includes:

[0031]

[0032] Where, χ is the eccentricity of the lens group under test, r is the radius of the circular trajectory, l12 is the distance between the image points of the on-axis light source and the off-axis light source on the first photodetector, f o is the focal length of the collimating lens group, l is the distance between the on-axis light source and the off-axis light source;

[0033] Calculate the focal length of the lens group under test, including:

[0034]

[0035] Where, f is the focal length of the lens group being tested, l 12 is the distance between the image points of the on-axis light source and the off-axis light source on the first photodetector, f o is the focal length of the collimating lens group, and l is the distance between the on-axis light source and the off-axis light source.

[0036] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0037] The present invention adopts a dual laser light source and introduces laser differential confocal technology to improve the accuracy and repeatability of the test; adopts a transmission light path to test complex lens groups and accurately measure the focal length and eccentricity of the lens / lens; the test device has strong resistance to environmental interference and good repeatability; it can realize automated and standardized testing of lens groups and reduce the influence of human factors on the test results. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a structural schematic diagram of a transmission-type lens eccentricity and focal length detection device based on differential confocal response of the present invention;

[0039] Figure 2 It is a working flow chart of the detection device in the present invention;

[0040] Figure 3 This is the optical path diagram of the eccentricity test of the lens group under test in the present invention;

[0041] Figure 4 is the differential response optical path diagram of the present invention;

[0042] Figure 5 It is a light path diagram for testing the focal length of the lens group under test in the present invention.

[0043] In the figure: 1-dual laser light source, 2-collimating lens group, 3-tested lens group, 4-air-suspended rotary lifting platform, 5-beam splitter, 6-first photodetector, 7-1:1 beam splitter, 8-pre-focus pinhole, 9-third photodetector, 10-post-focus pinhole, 11-second photodetector, 12-control system. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0045] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0046] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0047] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0048] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0049] The general reflective center deviation test device can only test the eccentricity and curvature of a single surface of the lens. For a lens group composed of multiple lenses, a transmissive center deviation test device is usually used. However, the position of the lens focus needs to be judged by the human eye or software algorithm for clarity, that is, the lens group or the photodetector position is adjusted along the optical axis, and the clearest graticule image is found on the display. When the graticule image is the clearest, it is considered that the focal plane of the lens coincides with the photodetector image plane, thereby obtaining the focal length value of the lens. However, this method is heavily dependent on individual judgment or the quality of the software algorithm, is easily affected by the environment, has poor test repeatability, and the test accuracy is limited by the resolution of the human eye / photodetector. In addition, different people have different criteria for judging the "clearest" position, making it difficult to form a unified standard.

[0050] The present invention proposes a transmission-type lens eccentricity and focal length detection device based on differential confocal response, and the device includes laser, collimating lens group, air suspension rotary lifting platform, spectroscope, photoelectric detector and other main components. The device uses a transmission light path to test the eccentricity and focal length of the lens group, and introduces laser differential confocal technology to determine the focal position, that is, two light paths with defocus amounts of +L and -L are used to detect the light intensity, and the results obtained by the detectors in the two light paths are subtracted, and a differential confocal curve is drawn according to the axial movement of the air suspension rotary lifting platform. The differential confocal curve passes through the zero point, indicating that the plane where the focus of the lens under test is located coincides with the plane where the defocus amount of the differential confocal light path is zero, and the next step of eccentricity and focal length test can be carried out. In the differential response light path, the response curve finally obtained is the result of subtracting the light intensity received by the two detectors, so the result eliminates the interference caused by the noise of the detector itself and the environment, improves the accuracy and repeatability of the test, and has strong anti-environmental interference ability.

[0051] In the eccentric test optical path, if the image point of the on-axis light source forms a circular trajectory as the air-suspended rotary lifting platform rotates, it indicates that the lens is eccentric. The radius of the circular trajectory at this time is recorded, and the position of the air-suspended rotary lifting platform is adjusted in the horizontal direction to make the circular trajectory become a point. The distance from this point to the main plane of the lens is the focal length of the lens. Since the internal structure of the packaged lens is unknown or relatively complex, the back intercept of the lens can be obtained by directly measuring the distance, but the position of the main plane cannot be determined. The present invention adopts a dual laser light source. In addition to the on-axis light source, an off-axis light source with a fixed distance from the on-axis light source is also set on the plane where the light source is located. The focal length of the lens under test can be calculated by the distance between the image points of the two light sources.

[0052] The present invention adopts a dual laser light source and introduces laser differential confocal technology to improve the accuracy and repeatability of the test; adopts a transmission light path to test complex lens groups; the test device has strong resistance to environmental interference and good repeatability; realizes automated and standardized testing of lens groups and reduces the influence of human factors on the test results.

[0053] like Figure 1 As shown, the transmission-type lens eccentricity and focal length detection device based on differential confocal response of an embodiment of the present application includes a dual laser light source 1, a collimating lens group 2, a lens group to be measured 3, an air-suspended rotary lifting platform 4, a spectrometer 5, a first photodetector 6, a 1:1 spectrometer 7, a pre-focus pinhole 8, a third photodetector 9, a post-focus pinhole 10, a second photodetector 11 and a control system 12.

[0054] The dual laser light source 1 is two identical lasers A and B. Laser A is on the central axis of the collimating lens group 2, the air suspension rotary lifting platform 4, the beam splitter 5, and the first photodetector 6. Laser B is on the same plane as laser A. The distance between laser A and laser B is a constant l. The laser beam becomes a parallel beam after passing through the collimating lens group 2. The lens group 3 to be tested is placed on the air suspension rotary lifting platform 4, so that the lens group 3 to be tested can rotate around the central axis of the collimating lens group 2, the air suspension rotary lifting platform 4, the beam splitter 5, and the first photodetector 6, and has the functions of lifting and lowering and horizontal movement, which is convenient for drawing the differential response curve. The beam splitter 5 divides the laser beam into two paths. The eccentricity and focal length values ​​of the lens group 3 to be tested are determined according to the position information of the laser point on the first photodetector 6. The 1:1 beam splitter 7, the pre-focus pinhole 8, the third photodetector 9, the post-focus pinhole 10, and the second photodetector 11 are differential confocal optical paths. The laser beam is split into two paths at a ratio of 1:1 through the 1:1 beam splitter 7, and enters the third photodetector 9 and the second photodetector 11 after passing through the pinhole. The defocus amounts of the photodetectors are +L and -L, respectively. The control system 12 controls the movement of the air-suspended rotary lifting platform 4, receives the signals of the three photodetectors, and analyzes and calculates the eccentricity and focal length of the lens group.

[0055] It should be noted that the lens group to be tested in the present application may be a single lens or a lens group consisting of multiple lenses.

[0056] Figure 2The following is a working flow chart of a transmissive lens eccentricity and focal length detection device based on differential confocal response. When testing, first turn on laser A, and the laser beam reaches the first photodetector 6, the second photodetector 11, and the third photodetector 9 after passing through the collimating lens group 2, the lens group to be tested 3, and the beam splitter 5; the air suspension rotary lifting platform 4 moves up and down along the central axis, and the defocusing amounts of the second photodetector 11 and the third photodetector 9 are +L and -L respectively. The difference between the intensity signals received by the second photodetector 11 and the third photodetector 9 and the amount of movement of the air suspension rotary lifting platform 4 can be used to draw a differential response curve. The curve passes through the zero point, indicating that the focal plane of the lens group to be tested 3 coincides with the light sensitive surface of the first photodetector 6. If a circular track appears on the first photodetector 6, the eccentricity of the lens group can be calculated from the radius of the circular track; the air suspension rotary lifting platform 4 is moved horizontally until the laser point no longer moves with the rotation of the lens group and the position remains fixed; turn on laser B, read the distance between the image points A1 and B1 of laser A and laser B on the first photodetector 6, and calculate the focal length of the lens group.

[0057] Figure 3 This is the optical path diagram for lens group eccentricity test. A1, A2, and A3 are the conjugate points of the laser light source A. The focal plane where A1 is located coincides with the light-sensitive surface of the first photodetector 6, while the second photodetector 11 and the third photodetector 9 do not coincide with the focal plane where A2 and A3 are located. The defocus amount of the light-sensitive surface of the second photodetector 11 is +L, and the defocus amount of the light-sensitive surface of the third photodetector 9 is -L. The function of the two defocus photodetectors is to record the light intensity of the two light spots, and use the intensity change of the light intensity signal to reflect the relative position of the focus of the tested lens and the light-sensitive surface of the first photodetector 6, thereby realizing high-precision fixed-focus measurement of the lens.

[0058] Let s be the normalized coordinate of the displacement of the air suspension rotary lift platform along the central axis, s L is the normalized coordinate of the defocus amount L of the photodetector, so the intensity signal I2(s,+s L ) and I3(s,-s L ) is subtracted to obtain the differential confocal intensity signal:

[0059]

[0060] It can be seen from the above formula that when the absolute values ​​of the defocus amounts of the second photodetector 11 and the third photodetector 9 are equal, the differential confocal intensity signal value is exactly zero, that is, Figure 4 Since A1, A2, and A3 are all conjugate points of the laser light source A, the corresponding A1, that is, the focus of the lens group under test, should coincide with the light sensitive surface of the first photodetector 6. The lens group rotates around the axis under the action of the air suspension rotary lifting platform. Figure 3As shown, if the lens group is not eccentric, A1 is exactly located in the center of the first photodetector 6; if the lens group is eccentric, as shown in A1', a circular trajectory is formed on the first photodetector 6, and the radius r of the circular trajectory is obtained by fitting, which is used to calculate the eccentricity of the lens group.

[0061] Figure 5 This is the optical path diagram for the focal length test of the lens group. After testing the lens eccentricity, adjust the air suspension rotary lift table to move the lens horizontally so that the laser point is located in the center of the first photodetector 6 and no longer forms a circular trajectory. Turn on laser B, and the conjugate point B1 of B appears on the first photodetector 6. Record the distance l between A1 and B1. 12 , the focal length of the lens group is:

[0062]

[0063] Among them, l 12 is the distance between A1 and B1 on the photodetector 1; f o is the focal length of the collimating lens group; l is the distance between lasers A and B.

[0064] The present invention adopts a transmission-type differential confocal optical path to test the focal length and eccentricity of the lens / lens, thereby realizing the test of the overall parameters of the complex lens group. In addition, the present invention uses a dual laser light source to test the focal length of the complex lens group, thereby simplifying the test structure and improving the test accuracy.

[0065] Specifically, the device consists of a light source, a collimating lens group, an air suspension lifting platform, a spectroscope, a photoelectric detector, and a control system. The light source is two identical lasers installed on the same plane. One laser A is located on the central axis of the collimating lens group, the air suspension lifting platform, and the photoelectric detector, and the distance between the other laser B and A is a constant value l. Figure 3 and Figure 4 As shown, after passing through the collimating lens group, the measured lens and the beam splitter, the conjugate points of A are A1, A2, and A3, and the conjugate point of B is B1. The focal plane where A1 and B1 are located coincides with the photodetector 1. The distance between the photosensitive surface of the photodetector 2 and A2 is +L, that is, the defocus amount is +L, and the distance between the photosensitive surface of the photodetector 3 and A3 is -L, that is, the defocus amount is -L. The air suspension lifting platform moves up and down along the central axis, and the intensity of the intensity signal received by the photodetector 2 and the photodetector 3 changes accordingly. The two signals are subtracted to obtain the differential confocal response curve. When the curve passes through the zero point, the corresponding position of the air suspension lifting platform is exactly the position where the lens focus coincides with the plane where the photodetector 1 is located. The position of the air suspension lifting platform is fixed at the zero point. At this time, the circular trajectory of the laser point on the photodetector 1 is fitted to obtain its radius r.

[0066] Adjust the horizontal position of the air suspension lifting platform so that the laser spot is located in the center of the photodetector 1 and no longer forms a circular trajectory. Turn on laser B, and a conjugate point B1 of B appears on the photodetector 1. Record the distance l between A1 and B1. 12 , the focal length of the lens group is:

[0067]

[0068] Lens group eccentricity:

[0069]

[0070] The focal length and eccentricity obtained by the transmission optical path test of the present invention are the result of the joint action of all lenses in the lens group, reflecting the characteristics of the entire lens, and can be used for auxiliary adjustment during the lens assembly process or quality inspection after the lens assembly is completed; different from the commonly used clarity focusing method, the present invention adopts a differential confocal optical path to identify the focus of the tested lens, thereby improving the test accuracy, and the test repeatability and anti-interference ability are strong; the motion control of the air-suspended lifting platform and the analysis of the test results of the three photoelectric detectors are all completed by the control system, realizing automated testing and improving detection efficiency.

[0071] In summary, the present invention proposes a transmissive lens eccentricity and focal length detection device based on differential confocal response, which can quickly detect the eccentricity and focal length of a lens group, has high accuracy and repeatability, and strong anti-interference ability, and is suitable for the assembly and inspection process of lenses, thereby improving the accuracy of lens assembly and inspection. The present invention designs the test device to be transmissive, so that it can test the focal length and eccentricity of a lens group composed of a single lens or multiple lenses, and uses a differential confocal optical path to identify the focus of the tested lens, thereby improving the test accuracy.

[0072] It should be noted that the order of the steps in the above embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0073] It should be pointed out that, according to the needs of implementation, the various steps / components described in this application can be split into more steps / components, and two or more steps / components or partial operations of steps / components can be combined into new steps / components to achieve the purpose of the present invention.

[0074] It will be easily understood by those skilled in the art that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A transmissive lens eccentricity and focal length detection device based on differential confocal response, characterized in that: The device comprises a dual laser light source, a collimating lens group, a lens group to be measured, an air-suspended rotary lifting platform, a beam splitter, a first photoelectric detector and a differential confocal optical path; The dual laser light source includes an on-axis light source and an off-axis light source with a constant distance from the on-axis light source, and the on-axis light source and the off-axis light source are on the same plane; the on-axis light source is located on the central axis of the collimating lens group, the air-suspended rotary lifting platform, the spectroscope and the first photodetector; the lens group to be tested is placed on the air-suspended rotary lifting platform, and the air-suspended rotary lifting platform enables the lens group to be tested to rotate around the central axis, rise and fall along the central axis, and move horizontally; the light beams of the dual laser light source are divided into two paths by the spectroscope, one path goes to the first photodetector, and the other path goes to the differential confocal optical path to draw a differential response curve; During the test, the on-axis light source is turned on first, and the light beam passes through the collimating lens group, the lens group to be tested and the beam splitter to reach the first photodetector and the differential confocal optical path; The air suspension rotary lifting platform moves up and down along the central axis, so that the lens group under test moves up and down along the central axis. The difference between the intensity signals received by the two detectors in the differential confocal optical path and the amount of movement of the air suspension rotary lifting platform are used to draw a differential response curve. The curve passes through the zero point, indicating that the focal plane of the lens group under test coincides with the light sensitive surface of the first photodetector at this time. The air-suspended rotary lifting platform rotates around the central axis to make the lens group under test rotate around the central axis; if a circular track appears on the first photoelectric detector, the eccentricity of the lens group under test is calculated according to the radius of the circular track; The air-suspended rotary lifting platform moves horizontally until the laser spot of the on-axis light source on the first photodetector no longer moves with the rotation of the lens group under test; the off-axis light source is turned on, the distance between the on-axis light source and the image point of the off-axis light source on the first photodetector is obtained, and the focal length of the lens group under test is calculated based on the distance between the on-axis light source and the off-axis light source and the distance between their image points.

2. The transmissive lens eccentricity and focal length detection device based on differential confocal response according to claim 1, characterized in that: The differential confocal optical path includes a 1:1 beam splitter, a pre-focus pinhole, a third photodetector, a post-focus pinhole and a second photodetector; The light beam to the differential confocal optical path is split into two paths again by a 1:1 beam splitter, one path passes through the pre-focus pinhole to the third photodetector, and the other path passes through the post-focus pinhole to the second photodetector. The defocus amounts of the second photodetector and the third photodetector are +L and -L, respectively.

3. The transmissive lens eccentricity and focal length detection device based on differential confocal response according to claim 2, characterized in that: The intensity signals received by the second photodetector and the third photodetector are subtracted to obtain a difference in intensity signals.

4. The transmissive lens eccentricity and focal length detection device based on differential confocal response according to claim 2, characterized in that: The device also includes a control system; The control system is used to control the movement of the air suspension rotary lifting platform, receive signals from the first photoelectric detector, the second photoelectric detector and the third photoelectric detector, and analyze and calculate the eccentricity and focal length of the measured lens group.

5. The transmissive lens eccentricity and focal length detection device based on differential confocal response according to claim 4, characterized in that: The control system is also used to control the on-axis light source and the off-axis light source to turn on and off.

6. The transmissive lens eccentricity and focal length detection device based on differential confocal response according to claim 1, characterized in that: The on-axis light source and the off-axis light source are two identical lasers.

7. The transmissive lens eccentricity and focal length detection device based on differential confocal response according to claim 1, characterized in that: Calculate the eccentricity of the lens group under test, including: Where, χ is the eccentricity of the lens group under test, r is the radius of the circular trajectory, l 12 is the distance between the image points of the on-axis light source and the off-axis light source on the first photodetector, f o is the focal length of the collimating lens group, and l is the distance between the on-axis light source and the off-axis light source.

8. The transmissive lens eccentricity and focal length detection device based on differential confocal response according to claim 1, characterized in that: Calculate the focal length of the lens group under test, including: Where, f is the focal length of the lens group being tested, l 12 is the distance between the image points of the on-axis light source and the off-axis light source on the first photodetector, f o is the focal length of the collimating lens group, and l is the distance between the on-axis light source and the off-axis light source.

9. A method for using the transmissive lens eccentricity and focal length detection device based on differential confocal response according to any one of claims 1 to 8, characterized in that: The following steps are involved: During the test, the on-axis light source is turned on first, and the light beam passes through the collimating lens group, the lens group to be tested and the beam splitter to reach the first photodetector and the differential confocal optical path; The air suspension rotary lifting platform moves up and down along the central axis, so that the lens group under test moves up and down along the central axis. The difference between the intensity signals received by the two detectors in the differential confocal optical path and the amount of movement of the air suspension rotary lifting platform are used to draw a differential response curve. The curve passes through the zero point, indicating that the focal plane of the lens group under test coincides with the light sensitive surface of the first photodetector at this time. The air-suspended rotary lifting platform rotates around the central axis to make the lens group under test rotate around the central axis; if a circular track appears on the first photoelectric detector, the eccentricity of the lens group under test is calculated according to the radius of the circular track; The air-suspended rotary lifting platform moves horizontally until the laser spot of the on-axis light source on the first photodetector no longer moves with the rotation of the lens group under test; the off-axis light source is turned on, the distance between the on-axis light source and the image point of the off-axis light source on the first photodetector is obtained, and the focal length of the lens group under test is calculated based on the distance between the on-axis light source and the off-axis light source and the distance between their image points.

10. The method of use according to claim 9, characterized in that: Calculate the eccentricity of the lens group under test, including: Where, χ is the eccentricity of the lens group under test, r is the radius of the circular trajectory, l t2 is the distance between the image points of the on-axis light source and the off-axis light source on the first photodetector, f o is the focal length of the collimating lens group, l is the distance between the on-axis light source and the off-axis light source; Calculate the focal length of the lens group under test, including: Where, f is the focal length of the lens group being tested, l 12 is the distance between the image points of the on-axis light source and the off-axis light source on the first photodetector, f o is the focal length of the collimating lens group, and l is the distance between the on-axis light source and the off-axis light source.

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