A flange focal length measuring device and method based on a double-ring grating

Abstract

The present invention discloses a flange focal length measuring device and method based on a double-ring grating, which includes a parallel light source, a plane mirror, a plane mirror driving module, an optical sensor and a control module. An annular moving grating, a collimator and a zero-position stage are sequentially arranged between the parallel light source and the plane mirror. The lens under test is installed on the zero-position stage. A beam splitter is arranged in the collimator. The light incident side of the beam splitter faces the lens under test, and an annular fixed grating is arranged between the light output side of the beam splitter and the optical sensor. The rotation mechanism of the annular moving grating, the plane mirror driving module and the optical sensor are respectively electrically connected to the control module. The control module is used to measure the flange focal length of the lens under test according to the electrical signal fed back by the optical sensor and the movement position of the plane mirror. The measuring device of the present invention has a simple structure, lower application cost, does not rely on complex algorithms, has a faster measurement speed, and effectively improves the measurement sensitivity of the flange focal length.

Description

Technical Field

[0001] The present invention relates to a lens flange focal length measuring device, and in particular to a flange focal length measuring device and method based on a double-ring grating. Background Art

[0002] The lens flange focal length refers to the distance between the imaging focal plane of the lens and the lens structure mounting surface. The flange focal length determines whether it is possible to focus at a specified object distance (usually infinity), and it is an important optical parameter to ensure clear imaging. Especially for the flange focal length of interchangeable lenses, it needs to match the flange distance of the camera body to work properly. In the actual production of lenses, due to factors such as the processing tolerance of the lens thickness and the deviation of the surface spacing caused by assembly, the consistency of the flange distance of the same type of lens is poor. Therefore, it is necessary to measure the position of the imaging focal plane and fine-tune and correct the position of the optical system in the lens housing (usually by rotating the thread or adding or subtracting spacer rings) according to the position deviation, so as to achieve the correct flange focal length.

[0003] In the prior art, the determination of the image focal plane of medium and short focal length lenses is mainly the parallel light focusing method. There are mainly two methods for searching the image focal plane. One is the reflection confocal method (pinhole illumination peak search) and the differential confocal focusing method, and the other is to use a micro camera to photograph the image focal plane, move the micro camera axially and continuously take pictures, and locate the image focal plane through methods such as the MTF peak search method and the gradient contrast peak search method. Among them, the reflection confocal method only collects defocus amount and imaging illumination information, and is fast, but has high requirements for the stability of the light source and the position of the confocal pinhole. The differential confocal focusing method significantly improves the focusing accuracy and sensitivity, but the system is relatively expensive, the test cost is high, and the test adjustment time is long. In addition, MTF and gradient contrast peak search, etc. need to collect a large number of images according to the change of defocus amount and perform a large number of calculations, resulting in a slow overall measurement speed. At the same time, for lenses with a large depth of focus, the measurement sensitivity will decrease significantly, making it difficult to search for the peak and resulting in a significant decrease in the focusing accuracy. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a flange focal length measuring device and method based on a double-ring grating with fast measurement speed, high measurement sensitivity and low application cost, aiming at the deficiencies of the prior art.

[0005] To solve the above technical problems, the present invention adopts the following technical solutions.

[0006] A flange focal length measuring device based on a double-ring grating, which comprises a parallel light source, a plane mirror driving module, an optical sensor and a control module. A plane mirror is provided at the moving end of the plane mirror driving module. An annular moving grating, a collimator and a zero-position stage are sequentially arranged between the parallel light source and the plane mirror. The zero-position stage is used for installing the lens to be measured. A beam splitter is arranged in the collimator. The light incident side of the beam splitter faces the lens to be measured, and an annular fixed grating is arranged between the light output side of the beam splitter and the optical sensor. The rotation mechanism of the annular moving grating, the plane mirror driving module and the optical sensor are respectively electrically connected to the control module. The control module is configured to: control the rotation mechanism of the annular moving grating to rotate at a constant speed; drive the plane mirror to reciprocate relative to the lens to be measured by controlling the movement of the plane mirror driving module; and measure the flange focal length of the lens to be measured according to the electrical signal fed back by the optical sensor and the movement position of the plane mirror.

[0007] Preferably, a plurality of sets of full-circle annular coarse gratings are provided on the annular moving grating. The annular radii of the plurality of sets of full-circle annular coarse gratings are different, and the plurality of sets of full-circle annular coarse gratings are concentrically distributed.

[0008] Preferably, the annular moving grating is located at the focal position of the collimator.

[0009] Preferably, a fixture for fixing the lens to be measured is provided on the zero-position stage, and the lens to be measured coincides with the zero-position surface of the zero-position stage.

[0010] Preferably, a plurality of sets of non-full-circle annular coarse gratings are provided on the annular fixed grating. The annular radii of the plurality of sets of non-full-circle annular coarse gratings are different, and the plurality of sets of non-full-circle annular coarse gratings are sequentially distributed along the circumferential direction of the annular fixed grating.

[0011] Preferably, the grating periods of the plurality of sets of full-circle annular coarse gratings are respectively the same as the grating periods of the plurality of sets of non-full-circle annular coarse gratings.

[0012] Preferably, the optical sensor is a photosensitive sensor. When the rotation mechanism of the annular moving grating rotates at a constant speed and the plane mirror driving module drives the plane mirror to reciprocate, the optical sensor outputs a sine wave voltage signal to the control module.

[0013] A method for measuring flange focal length based on a double-ring grating. This method is implemented based on the above-mentioned device, and the method includes: Tuning step: Adjust the plane mirror and the fixed-ring grating to a preset initial position; Loading step: Load the lens under test onto the zero-position stage and make the lens under test coincide with the zero-position surface of the zero-position stage; Control step: The control module controls the rotary motion mechanism of the moving-ring grating to rotate at a constant speed, and drives the plane mirror to reciprocate relative to the lens under test by controlling the movement of the plane mirror drive module; Calculation step: The control module receives the sinusoidal voltage signal fed back by the optical sensor, and measures the flange focal length of the lens under test in combination with the movement position of the plane mirror.

[0014] Preferably, a plurality of groups of non-full-circle annular coarse gratings are provided on the fixed-ring grating. In the tuning step: The control module controls the rotary motion mechanism of the fixed-ring grating to rotate until the specified non-full-circle annular coarse grating rotates to the light-incident side of the optical sensor; While the control module controls the movement of the plane mirror drive module, the micrometer is used to measure the distance difference between the reflecting surface of the plane mirror and the preset zero position of the device until the distance difference meets the preset distance requirement.

[0015] Preferably, in the calculation step: While the optical sensor outputs a sinusoidal voltage signal to the control module, the control module records the displacement a of the plane mirror relative to the zero position of the device, then: The displacement a corresponding to the amplitude peak value of the sinusoidal voltage signal is the flange focal length of the lens under test 5.

[0016] In the flange focal length measuring device based on a double-ring grating disclosed in the present invention, first, the plane mirror and the fixed-ring grating are adjusted to a preset initial position, then the lens under test is loaded onto the zero-position stage and the lens under test coincides with the zero-position surface of the zero-position stage. During the measurement process, the control module controls the rotary motion mechanism of the moving-ring grating to rotate at a constant speed, and at the same time controls the movement of the plane mirror drive module. The plane mirror drive module drives the plane mirror to reciprocate relative to the lens under test. Based on the cooperation of the moving-ring grating and the plane mirror drive module, the control module receives the sinusoidal voltage signal fed back by the optical sensor, and then measures the flange focal length of the lens under test in combination with the movement position of the plane mirror. Compared with the measurement methods in the prior art, the structure of the measurement device of the present invention is simple, the application cost is lower, and it does not rely on complex algorithms, and the measurement speed is faster, effectively improving the measurement sensitivity of the flange focal length. Description of the Drawings

[0017] Figure 1Schematic structural diagram of the flange focal length measuring device based on a double-ring grating according to the present invention;

[0018] Figure 2 Schematic structural diagram of the movable ring grating;

[0019] Figure 3 Schematic structural diagram of the fixed ring grating;

[0020] Figure 4 Waveform diagram of the sinusoidal voltage signal output by the optical sensor. Specific implementation mode

[0021] The present invention will be described in more detail below in conjunction with the accompanying drawings and embodiments.

[0022] The present invention discloses a flange focal length measuring device based on a double-ring grating. As shown in combination with Figures 1 to 4 , it includes a parallel light source 1, a plane mirror driving module 7, an optical sensor 10 and a control module 8. A plane mirror 6 is provided at the moving end of the plane mirror driving module 7. Between the parallel light source 1 and the plane mirror 6, there are successively arranged a movable ring grating 2, a collimator 4 and a zero position stage 11. The zero position stage 11 is used to mount the lens under test 5. A beam splitter 3 is provided in the collimator 4. The light incident side of the beam splitter 3 faces the lens under test 5, and a fixed ring grating 9 is provided between the light output side of the beam splitter 3 and the optical sensor 10. The rotation mechanism of the movable ring grating 2, the plane mirror driving module 7 and the optical sensor 10 are respectively electrically connected to the control module 8. The control module 8 is used for:

[0023] Controlling the rotation mechanism of the movable ring grating 2 to rotate at a constant speed;

[0024] Driving the plane mirror 6 to reciprocate relative to the lens under test 5 by controlling the movement of the plane mirror driving module 7;

[0025] And measuring the flange focal length of the lens under test 5 according to the electrical signal fed back by the optical sensor 10 and the movement position of the plane mirror 6.

[0026] In the above device, first, the plane mirror 6 and the annular fixed grating 9 are adjusted to preset initial positions. Then, the lens under test 5 is loaded onto the zero-position stage 11, and the lens under test 5 is made to coincide with the zero-position surface of the zero-position stage 11. During the measurement process, the rotation mechanism of the annular moving grating 2 is controlled by the control module 8 to rotate at a constant speed, and at the same time, the movement of the plane mirror driving module 7 is controlled. The plane mirror driving module 7 drives the plane mirror 6 to reciprocate relative to the lens under test 5. Based on the cooperation of the annular moving grating 2 and the plane mirror driving module 7, the control module 8 receives the sine-wave voltage signal fed back by the optical sensor 10, and then combines with the movement position of the plane mirror 6 to measure and obtain the flange focal length of the lens under test 5. Compared with the measurement methods in the prior art, the measurement device of the present invention has a simple structure, lower application cost, does not rely on complex algorithms, has a faster measurement speed, and effectively improves the measurement sensitivity of the flange focal length.

[0027] Please refer to Figure 2 , regarding the preferred structure of the annular moving grating 2, in this embodiment, a plurality of full-circle annular coarse gratings 20 are provided on the annular moving grating 2. The annular radii of the plurality of full-circle annular coarse gratings 20 are different, and the plurality of full-circle annular coarse gratings 20 are concentrically distributed. In practical applications, the grating part of the annular moving grating 2 is illuminated by the parallel light source 1. Figure 2 The black area shown in

[0028] Specifically, the annular moving grating 2 is located at the focal position of the collimator 4 or the position corresponding to a specified object distance. The rotation mechanism of the annular moving grating 2 is realized by a motor drive mode. The light emitted by the annular moving grating 2 passes through the lens of the collimator 4 and is equivalent to an infinite object distance (or a specified object distance), and then passes through the lens under test 5 and forms an image on the image focal plane of the lens under test 5.

[0029] As a preferred method, a fixture for fixing the lens under test 5 is provided on the zero-position stage 11, and the lens under test 5 coincides with the zero-position surface of the zero-position stage 11. Among them, the lens under test 5 is fixed on the zero-position stage 11 of the device through the fixture. After the lens under test 5 is installed, it should be coaxial with the collimator 4, and it is required that the flange surface of the lens under test 5 coincides with the zero plane of the device.

[0030] Regarding the driving method of the planar mirror 6, in this embodiment, the planar mirror 6 is driven by a planar mirror driving module 7 to move axially, that is, to reciprocally perform approaching and departing actions relative to the lens under test 5. When the reflecting surface of the planar mirror 6 coincides with the image focal plane of the lens under test 5, the imaging optical path returns along the original path, and then is reflected by the beam splitter 3 at the annular fixed grating 9 to form a real image equal in size to the annular moving grating 2.

[0031] In this embodiment, the annular fixed grating 9 is provided with multiple groups of non-full-circle annular coarse gratings 90. The annular radii of the multiple groups of non-full-circle annular coarse gratings 90 are different, and the multiple groups of non-full-circle annular coarse gratings 90 are sequentially distributed along the circumferential direction of the annular fixed grating 9.

[0032] Furthermore, the grating periods of the multiple groups of full-circle annular coarse gratings 20 are respectively the same as those of the multiple groups of non-full-circle annular coarse gratings 90.

[0033] In practical applications, the annular moving grating 2 and the annular fixed grating 9 are in conjugate positions corresponding to each other. Please refer to Figure 3 , Figure 3 In the annular fixed grating 9 described in, the black area is a light-transmitting area. The annular fixed grating 9 is also installed at the rotating end of a preset rotating motion mechanism. Its main function is to select a coarse grating with a suitable period according to the different focal lengths and sharpness of the lens under test 5, thereby improving the measurement accuracy.

[0034] Please refer to Figure 4 , in this embodiment, the optical sensor 10 is a photosensitive sensor. When the rotating motion mechanism of the annular moving grating 2 rotates at a constant speed and the planar mirror driving module 7 drives the planar mirror 6 to reciprocate, the optical sensor 10 outputs a sine-wave voltage signal to the control module 8. The specific principle is as follows:

[0035] The equal-sized real image of the annular moving grating 2 interferes with the annular fixed grating 9, presenting an enlarged Moiré fringe. During the continuous and uniform rotation of the annular moving grating 2, the equal-sized real image of the annular moving grating 2 also rotates at a constant speed, and the Moiré fringe formed by the interference with the annular fixed grating 9 presents continuous movement. The optical sensor 10 converts the brightness change of the Moiré fringe into a voltage signal, obtaining a voltage signal approximate to a sine wave;

[0036] When the reflecting surface of the planar mirror 6 moves away from the imaging focal plane of the lens under test 5, the equal-sized real image of the annular moving grating 2 becomes blurred, the contrast of the bright and dark areas decreases, and at the same time, the standard shape of the grating cannot be maintained, and the Moiré fringe formed by the interference with the annular fixed grating 9 gradually disappears. The amplitude of the sine-wave voltage signal obtained by the control module 8 from the optical sensor 10 gradually decreases.

[0037] During the process of the control module 8 controlling the movement of the plane mirror 6, the displacement of the plane mirror 6 is recorded in real time. Meanwhile, the voltage signal output by the optical sensor 10 is collected at a high frequency. A signal amplification circuit is provided in the control module 8 to amplify and filter the voltage signal output by the optical sensor 10. An A / D conversion module is also provided in the control module 8, which can convert the voltage signal into digital information and has a calculation function to search for the amplitude peak value of the voltage digital information. The key process is that when the amplitude of the sine wave voltage signal is the largest, the position of the reflecting surface of the plane mirror 6 is the image focal plane of the lens to be measured, and the distance between the position of the reflecting surface of the plane mirror 6 and the zero position of the device is the flange focal length of the lens to be measured 5.

[0038] Based on the above hardware architecture of the device, the present invention also discloses a method for measuring the flange focal length based on a double-ring grating, combined with Figures 1 to 4 As shown, this method is implemented based on the above device, and the method includes:

[0039] Calibration step: Adjust the plane mirror 6 and the annular fixed grating 9 to a preset initial position;

[0040] Loading step: Load the lens to be measured 5 on the zero position stage 11 and make the lens to be measured 5 coincide with the zero position surface of the zero position stage 11;

[0041] Control step: The control module 8 controls the rotation mechanism of the annular moving grating 2 to rotate at a constant speed, and drives the plane mirror 6 to reciprocate relative to the lens to be measured 5 by controlling the movement of the plane mirror driving module 7;

[0042] Calculation step: The control module 8 receives the sine wave voltage signal fed back by the optical sensor 10 and measures the flange focal length of the lens to be measured 5 in combination with the movement position of the plane mirror 6.

[0043] Further, a plurality of groups of non-full-circle annular coarse gratings 90 are provided on the annular fixed grating 9. In the calibration step:

[0044] The control module 8 controls the rotation mechanism of the annular fixed grating 9 to rotate until the specified non-full-circle annular coarse grating 90 is rotated to the light incident side of the optical sensor 10;

[0045] While the control module 8 controls the movement of the plane mirror driving module 7, a micrometer is used to measure the distance difference between the reflecting surface of the plane mirror 6 and the preset zero position of the device until the distance difference meets the preset distance requirement.

[0046] In addition, in the above-mentioned calculation steps: while the optical sensor 10 outputs a sine-wave voltage signal to the control module 8, the control module 8 records the displacement a of the plane mirror 6 relative to the zero position of the device, then:

[0047] The displacement a corresponding to the amplitude peak of the sine-wave voltage signal is the flange focal length of the measured lens 5.

[0048] In a preferred embodiment of the present invention, the flange focal length measurement method based on a double-ring grating can refer to the following specific embodiments:

[0049] Embodiment 1

[0050] This embodiment is a measurement method of a flange focal length measurement device using a double-ring grating, including the following steps:

[0051] Step S1, zero position calibration. At this time, the measured lens 5 is not installed. The control module 8 controls the plane mirror 6 to move to the zero position of the device, and uses a micrometer to measure the distance difference between the reflecting surface of the plane mirror 6 and the zero position of the device. The control module 8 controls the plane mirror 6 to move until the distance difference is 0 or below a specific accuracy. At this time, the position of the plane mirror 6 is reset to zero.

[0052] Step S2, select the grating period. According to the focal length and clarity of the measured lens 5, the control module 8 controls the rotation of the fixed-ring grating 9 so that the grating with an appropriate grating period on the fixed-ring grating 9 rotates in front of the photosensitive sensor and remains fixed.

[0053] Step S3, install the measured lens 5, and make the flange surface of the measured lens 5 coincide with the zero position of the device.

[0054] Step S4, the control module 8 controls the continuous and uniform rotation of the moving-ring grating 2.

[0055] Step S5, the control module 8 controls the plane mirror 6 to move quickly in the full stroke (or a specified stroke), and at the same time, high-frequency samples the voltage signal output by the photosensitive sensor and converts it into a digital signal, obtaining a set of corresponding data composed of the position of the plane mirror 6 and the voltage signal of the photosensitive sensor.

[0056] Step S6, the control module 8 analyzes and calculates the data obtained in step S5, and records the position of the plane mirror 6 corresponding to the amplitude peak of the sine-wave voltage signal as a. Then a is the flange focal length of the measured lens 5.

[0057] Compared with the prior art, the present invention converts the clarity and contrast of lens imaging into voltage signals that are easy to collect and analyze, greatly reducing the amount of calculation, effectively improving the test sensitivity and accuracy, while also reducing the measurement time and enhancing the test efficiency. It is particularly suitable for quality control of the flange focal length of lenses on the lens production line. In addition, the present invention can quickly and accurately measure the flange focal length of a lens. If combined with a lens focusing mechanism, it can efficiently produce lenses with a specified flange focal length, adapt to CMOS or CCD sensor components that have been pasted and have their heights measured, and achieve the goal of focusing immediately after assembly or high-precision pre-focusing.

[0058] The above are only preferred embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, or improvements made within the technical scope of the present invention shall be included within the scope protected by the present invention.

Claims

1. A flange focal length measuring device based on a double-ring grating, characterized in that It includes a parallel light source (1), a plane mirror driving module (7), an optical sensor (10) and a control module (8). A plane mirror (6) is provided at the moving end of the plane mirror driving module (7). An annular moving grating (2), a collimator (4) and a zero position stage (11) are successively arranged between the parallel light source (1) and the plane mirror (6). The zero position stage (11) is used to mount the lens under test (5). A beam splitter (3) is provided in the collimator (4). The light incident side of the beam splitter (3) faces the lens under test (5). An annular fixed grating (9) is provided between the light output side of the beam splitter (3) and the optical sensor (10). The rotation mechanism of the annular moving grating (2), the plane mirror driving module (7) and the optical sensor (10) are respectively electrically connected to the control module (8). The control module (8) is used for: Controlling the rotation mechanism of the annular moving grating (2) to rotate at a constant speed; Driving the plane mirror (6) to reciprocate relative to the lens under test (5) by controlling the movement of the plane mirror driving module (7); And measuring the flange focal length of the lens under test (5) according to the electrical signal fed back by the optical sensor (10) and the movement position of the plane mirror (6); Multiple groups of full - circumference annular coarse gratings (20) are provided on the annular moving grating (2). The annular radii of the multiple groups of full - circumference annular coarse gratings (20) are different, and the multiple groups of full - circumference annular coarse gratings (20) are concentrically distributed; The annular moving grating (2) is located at the focal position of the collimator (4); Multiple groups of non - full - circumference annular coarse gratings (90) are provided on the annular fixed grating (9). The annular radii of the multiple groups of non - full - circumference annular coarse gratings (90) are different, and the multiple groups of non - full - circumference annular coarse gratings (90) are successively distributed along the circumference of the annular fixed grating (9); The grating periods of the multiple groups of full - circumference annular coarse gratings (20) are respectively the same as the grating periods of the multiple groups of non - full - circumference annular coarse gratings (90).

2. The flange focal length measuring device based on a double-ring grating according to claim 1, characterized in that A fixture for fixing the lens under test (5) is provided on the zero position stage (11), and the lens under test (5) coincides with the zero position surface of the zero position stage (11).

3. The flange focal length measuring device based on a double-ring grating according to claim 1, characterized in that, The optical sensor (10) is a photosensitive sensor. When the rotation mechanism of the annular moving grating (2) rotates at a constant speed and the plane mirror driving module (7) drives the plane mirror (6) to reciprocate, the optical sensor (10) outputs a sine - wave voltage signal to the control module (8).

4. A method for measuring the flange focal length based on a double-ring grating, characterized in that, This method is implemented based on the device according to any one of claims 1 to 3. The method includes: Calibration step: Adjusting the plane mirror (6) and the annular fixed grating (9) to a preset initial position; Loading step: Loading the lens under test (5) onto the zero position stage (11) and making the lens under test (5) coincide with the zero position surface of the zero position stage (11); Control step: The control module (8) controls the rotary motion mechanism of the annular moving grating (2) to rotate at a constant speed, and drives the plane mirror (6) to reciprocate relative to the lens under test (5) by controlling the movement of the plane mirror driving module (7); Calculation step: The control module (8) receives the sine wave voltage signal fed back by the optical sensor (10), and measures the flange focal length of the lens under test (5) in combination with the movement position of the plane mirror (6).

5. The method for measuring the flange focal length based on a double-ring grating according to claim 4, wherein, In the calibration step: The control module (8) controls the rotary motion mechanism of the annular fixed grating (9) to rotate until the specified non-full-circle annular coarse grating (90) is rotated to the light incident side of the optical sensor (10); While the control module (8) controls the movement of the plane mirror driving module (7), the micrometer is used to measure the distance difference between the reflecting surface of the plane mirror (6) and the preset zero position of the device until the distance difference meets the preset distance requirement.

6. The flange focal length measurement method based on a double-ring grating according to claim 5, characterized in that In the calculation step: While the optical sensor (10) outputs a sine wave voltage signal to the control module (8), the control module (8) records the displacement a of the plane mirror (6) relative to the zero position of the device, then: The displacement a corresponding to the amplitude peak value of the sine wave voltage signal is the flange focal length of the lens under test (5).

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