Three-degree-of-freedom angle measuring device and method based on radial polarized light

Abstract

The invention relates to the technical field of laser quantum interference measurement, in particular to a three-degree-of-freedom angle measurement device and method based on radial polarized light, which can realize high-precision simultaneous measurement of three-degree-of-freedom tiny angles by utilizing the characteristics of the radial polarized light and combining an advanced optical system and a signal processing technology. By adopting an auto-collimation technology principle, the tight focusing characteristic of radial polarized light and the light splitting characteristic of a Wollaston prism are combined, so that technical indexes such as angle measurement resolution and angle measurement precision can be effectively improved; the roll angle measuring system formed by using the focusing characteristic of the all-dielectric super-lens array and the CCD camera can greatly improve the roll angle measuring precision of the existing method.

Description

Technical Field

[0001] The present invention relates to the technical field of laser quantum interference measurement, and in particular to a three-degree-of-freedom angle measurement device and method based on radially polarized light. Background Art

[0002] In the field of optical engineering, the measurement of tiny angles is crucial for the calibration of optical systems, precise control of light beams, and precise positioning of optical components. In the fields of precision machinery and aerospace, tiny angle changes may lead to performance degradation of mechanical components or deviation of the flight trajectory of aerospace vehicles. At present, the accuracy and stability requirements for tiny angle measurements are getting higher and higher. Traditional angle measurement methods, such as photoelectric encoders and optical interferometry, have problems such as limited accuracy and insufficient stability when measuring tiny angles. Therefore, exploring new ways to measure tiny angles has become an important research direction.

[0003] In summary, the current three-degree-of-freedom angle measurement technology has disadvantages such as low measurement accuracy and complex system. Summary of the invention

[0004] In view of this, the present invention provides a three-degree-of-freedom angle measurement device and method based on radially polarized light, which can utilize the characteristics of radially polarized light, combine advanced optical systems and signal processing technology, and achieve high-precision simultaneous measurement of three-degree-of-freedom tiny angles.

[0005] To achieve the above purpose, the technical solution of the present invention is as follows:

[0006] A three-degree-of-freedom angle measurement device based on radial polarized light, comprising a radial polarized light system, a polarizing prism, a first Wave plate, total reflection mirror, second Wave plate, SLM, measuring target mirror, first prism, wavefront detector, wavefront controller, second prism, pitch angle and yaw angle measurement system and roll angle measurement system;

[0007] The radial polarization light system generates radial polarized light, which is incident on the polarization prism;

[0008] The horizontal light transmitted by the polarizing prism is incident on the SLM, and after being reflected by the SLM, it reaches the measuring target mirror fixed on the target to be measured. The measuring target mirror reflects the incident light and passes through the SLM and the second The wave plate is incident on the polarizing prism, and then reflected by the polarizing prism and passes through the first After the wave plate, it reaches the total reflection mirror, and then passes through the first wave plate, then passes through the polarizing prism before entering the first prism;

[0009] The vertical light reflected by the polarizing prism is incident on the first prism;

[0010] The reflected light from the first prism is incident on the wavefront detector, and the wavefront information detected by the wavefront detector is fed back to the wavefront controller, and the wavefront controller generates a control signal and applies it to the SLM;

[0011] The transmitted light through the first prism is incident on the second prism for spectroscopic analysis; the transmitted light through the second prism is incident on the pitch angle and yaw angle measurement system to measure the pitch angle and yaw angle; the reflected light through the second prism is incident on the roll angle measurement system to measure the roll angle.

[0012] It also includes a computer; the pitch angle and yaw angle measurement system includes a Wollaston prism, a third lens, a fourth lens, a first position sensitivity detector and a second position sensitivity detector; wherein, after being transmitted through the first beam splitter prism, the transmitted light is split by the second beam splitter prism, and the transmitted light through the second beam splitter prism reaches the Wollaston prism. After being split by the Wollaston prism, one beam of light is focused to the first position sensitivity detector through the third lens, and the other beam of light is focused to the second position sensitivity detector through the fourth lens, so that the focal position of the target to be measured when it is stationary and the focal position after the angle changes are obtained on the two position sensitivity detectors, and the numerical output of the pitch angle and yaw angle is obtained after being calculated and processed by the computer according to the formula.

[0013] The roll angle measurement system includes an all-dielectric superlens array, a fifth lens and a CCD camera. The reflected light from the second beam splitter is incident on the all-dielectric superlens array. The all-dielectric superlens array includes multiple pixels, each pixel includes two different superlenses, and can separate two different polarization components from the incident light beam. After passing through the fifth lens, the light spot is focused on the CCD camera, and the focal spot positions in the static state and after the angle change are obtained respectively. The CCD camera is used in combination with the all-dielectric superlens array to indirectly measure and calculate the change of the focal position, thereby obtaining the roll angle by measuring and calculating the focal position. The CCD camera receives the signal and transmits it to the computer, and the computer processes it to obtain the numerical output of the roll angle.

[0014] The front surface of the CCD camera and the front surface of the measuring target mirror are perpendicular to each other, and position calibration is performed when they are placed.

[0015] Among them, the all-dielectric superlens array regulates the propagation and focusing behavior of the incident light by designing the subwavelength structure on the dielectric surface.

[0016] Among them, the radial polarization light system includes a laser, an S wave plate, a first lens and a second lens; the laser generates linear polarized light, which is converted into radial polarized light after passing through the S wave plate, and the radial polarized light is expanded by a beam expansion system composed of a first lens and a second lens, and then incident on a polarization prism for splitting.

[0017] The present invention also provides a three-degree-of-freedom angle measurement method based on radially polarized light, which uses the device of the present invention to implement the measurement, and includes the following steps:

[0018] The signals received by the first position sensitivity detector, the second position sensitivity detector and the CCD camera are transmitted to the computer, and are processed by the computer to obtain numerical outputs of the pitch angle, the yaw angle and the roll angle.

[0019] The calculation formula of the pitch angle is:

[0020]

[0021] The calculation formula of the yaw angle is:

[0022]

[0023] In the formula, X PSD1 and Y PSD1 are respectively the focal spot positions in the horizontal and vertical directions of the first position sensitive detector and the second position sensitive detector in a static state; X PSD2 and Y PSD2 are respectively the focal spot positions in the horizontal and vertical directions of the first position sensitive detector and the second position sensitive detector after the angle change occurs; f1 and f2 are respectively the focal lengths of the third lens and the fourth lens.

[0024] The calculation formula of the roll angle is:

[0025]

[0026] In the formula, Z PSD1 Z is the focal spot position in the vertical direction of the CCD camera in a static state; PSD2 is the focal spot position in the vertical direction of the CCD camera after the angle change; f3 is the focal length of the fifth lens.

[0027] Beneficial effects:

[0028] 1. The prior art usually adopts laser interference, autocollimation measurement and visual measurement to obtain the pitch angle and yaw angle. The device of the present invention adopts the principle of autocollimation technology, combines the tight focusing characteristics of radially polarized light with the spectral characteristics of Wollaston prism, and can effectively improve the technical indicators such as angle measurement resolution and angle measurement accuracy. The prior art usually adopts electronic level and other methods to measure the roll angle. The device of the present invention utilizes the focusing characteristics of the all-dielectric superlens array and the CCD camera to form a roll angle measurement system, which can greatly improve the measurement accuracy of the roll angle of the existing method.

[0029] 2. In the prior art, when performing angle measurement, it is usually rare to compensate for the angle error caused by environmental interference when the target is in a stationary state. The device of the present invention uses a wavefront detector, a wavefront controller and a spatial light modulator SLM to compensate for the distortion caused by environmental interference (such as vibration and temperature change) by adjusting the slight deformation of the SLM mirror in real time. This adjustment can compensate for the three-degree-of-freedom angle error signal in a stationary state.

[0030] 3. The device of the present invention adopts the principle of laser self-collimation, and realizes the compensation of the angle error signal of the target to be measured in a static state by utilizing a spatial light modulator SLM, a wavefront detector and a wavefront controller; by combining the tight focusing characteristics of radially polarized light and the spectral characteristics of a Wollaston prism, the focal spot position on the position-sensitive detector is analyzed to realize the measurement of the pitch angle and the yaw angle; by utilizing the measurement principle that the pitch angle in one direction is the roll angle in the direction perpendicular to it, by utilizing the focusing characteristics of an all-dielectric superlens array and a CCD camera, the focal spot position on the CCD camera is analyzed to realize the measurement of the roll angle, and the three-degree-of-freedom angle measurement results are processed and analyzed by a computer and then output, which can effectively improve the measurement resolution of small angles of the three degrees of freedom, the angle measurement accuracy and other technical indicators.

[0031] 4. The method of the present invention is implemented based on the device of the present invention. It adopts the principle of self-collimation technology and combines the tight focusing characteristics of radially polarized light with the spectral characteristics of Wollaston prism, which can effectively improve technical indicators such as angle measurement resolution and angle measurement accuracy. The rolling angle measurement system formed by utilizing the focusing characteristics of the all-dielectric superlens array and the CCD camera can greatly improve the measurement accuracy of the rolling angle of the existing method.

[0032] 5. The method of the present invention is implemented based on the device of the present invention, using a wavefront detector, a wavefront controller and a spatial light modulator SLM, and adjusting the slight deformation of the SLM mirror in real time to compensate for the distortion caused by environmental interference (such as vibration and temperature change, etc.). This adjustment can compensate for the three-degree-of-freedom angle error signal in a static state.

[0033] 6. The method of the present invention adopts the principle of laser self-collimation, and realizes the compensation of the angle error signal of the target to be measured in a static state by utilizing a spatial light modulator SLM, a wavefront detector and a wavefront controller; by combining the tight focusing characteristics of radially polarized light and the spectral characteristics of a Wollaston prism, the focal spot position on a position-sensitive detector is analyzed to realize the measurement of the pitch angle and the yaw angle; by utilizing the measurement principle that the pitch angle in one direction is the roll angle in a direction perpendicular to it, by utilizing the focusing characteristics of an all-dielectric superlens array and a CCD camera, the focal spot position on the CCD camera is analyzed to realize the measurement of the roll angle, and the three-degree-of-freedom angle measurement results are processed and analyzed by a computer and then output, which can effectively improve the measurement resolution of small angles of the three degrees of freedom, the angle measurement accuracy and other technical indicators. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic structural diagram of the three-degree-of-freedom angle measurement device based on radially polarized light of the present invention. DETAILED DESCRIPTION

[0035] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0036] As a special form of light field distribution, radially polarized light has a characteristic of strong light intensity at the center and weak light intensity at the edge, and the light field direction is distributed radially. This unique property makes radially polarized light have potential advantages in measuring small angles. The present invention provides a three-degree-of-freedom angle measurement device based on radially polarized light, the structure of which is as follows: Figure 1 As shown, it includes: a laser (1), an S wave plate (2), a first lens (3), a second lens (4), a polarizing prism (5), a first quarter Wave plate (6), total reflection mirror (7), second quarter A wave plate (8), a spatial light modulator SLM (9), a measuring target mirror (10), a first beam splitter prism (11), a wavefront detector (12), a wavefront controller (13), a second beam splitter prism (14), a Wollaston prism (15), a third lens (16), a fourth lens (17), a first position sensitivity detector (18), a second position sensitivity detector (19), an all-dielectric super lens array (20), a fifth lens (21), a CCD camera (22) and a computer (23); wherein the Wollaston prism (15), the third lens (16), the fourth lens (17), the first position sensitivity detector (18) and the second position sensitivity detector (19) form a pitch angle and yaw angle measurement system to achieve measurement of the pitch angle and yaw angle; and the all-dielectric super lens array (20), the fifth lens (21) and the CCD camera (22) form a roll angle measurement system to achieve measurement of the roll angle.

[0037] The laser (1) generates linearly polarized light, which is converted into radially polarized light after passing through an S wave plate (2). The radially polarized light is expanded by a beam expansion system composed of a first lens (3) and a second lens (4), and then incident on a polarization prism (5) for light splitting.

[0038] Horizontal light (P light) transmitted through the polarizing prism (5) is incident on the spatial light modulator SLM (9), and reaches the measuring target mirror (10) after being reflected by the spatial light modulator SLM (9). The surface of the measuring target mirror (10) is plated with a total reflection film, thereby achieving total reflection of the incident light. The measuring target mirror (10) is fixed on the target to be measured, and when the target to be measured moves, the measuring target mirror (10) will move along with it, and then the measurement of the changing angle of the target to be measured is achieved by measuring the measuring target mirror. The light reflected by the measuring target mirror (10) passes through the spatial light modulator SLM (9) and the second quarter wave plate (8) again, and the reflected light carries information on the change in the angle position. As the light passes through the second quarter wave plate (8) twice, the horizontal light (P light) is converted into the vertical light (S light). The vertical light (S light) is incident on the polarizing prism (5), and after being reflected by the polarizing prism (5), it passes through the first quarter wave plate (6) and reaches the total reflection mirror (7). After being reflected by the total reflection mirror (7), it passes through the first quarter wave plate (6) again. As the light passes through the first quarter wave plate (6) twice, the vertical light (S light) is converted into the horizontal light (P light). The horizontal light (P light) passes through the polarizing prism (5) and is incident on the first beam splitting prism (11).

[0039] The vertical light (S light) reflected by the polarizing prism (5) is incident on the first beam splitting prism (11) for beam splitting.

[0040] The reflected light (with angle change information) from the first beam splitter (11) is incident on a wavefront detector (12) for detection, and the detected wavefront information (such as the slope or curvature distribution of the phase disturbance caused by the angle change) is fed back to a wavefront controller (13). The information is processed by an algorithm inside the wavefront controller (13) and converted into phase information, thereby realizing wavefront reconstruction. The main purpose of this step is to obtain the complete phase distribution of the wavefront before distortion. The wavefront controller (13) generates control signals through a control algorithm according to the phase distribution of the distorted wavefront. These control signals are finally applied to the spatial light modulator SLM (9) through digital-to-analog conversion and a high-voltage amplifier. The spatial light modulator SLM (9) changes the direction of the reflected light beam according to these control signals through the feedback state control of the spatial light modulator SLM (9), thereby achieving the purpose of correcting the wavefront. Since the spatial light modulator SLM (9) can be used to adjust the slight deformation of the mirror in real time to compensate for the distortion caused by environmental interference (such as vibration and temperature change). This adjustment can realize the compensation of the three-degree-of-freedom angle error signal in a static state. Purpose of compensation: When the target to be measured is in a static state, environmental interference will cause the target to produce a small angle change, which will cause errors in the angle measurement. Therefore, it is necessary to compensate for the small angle change of the target to be measured in a relatively static state. It should be noted that the prerequisite for angle error compensation is to set an angle threshold in advance. When the angle change caused by environmental interference is less than the set angle threshold, the angle error is compensated. When the angle change caused by environmental interference is greater than the set angle threshold, it is not compensated. The purpose of setting the angle threshold is to avoid the system from compensating for the small angle that the target to be measured itself needs to measure when measuring small angles. The angle threshold is set according to the angle measurement accuracy that needs to be obtained.

[0041] The transmitted light through the first beam splitter prism (11) is incident on the second beam splitter prism (14) for beam splitting; the transmitted light through the second beam splitter prism (14) is incident on the pitch angle and yaw angle measurement system to achieve measurement of the pitch angle and yaw angle; the reflected light through the second beam splitter prism (14) is incident on the roll angle measurement system to achieve measurement of the roll angle. The first beam splitter prism (11) and the second beam splitter prism (14) both have different beam splitting ratios.

[0042] In the pitch angle and yaw angle measurement system including a Wollaston prism (15), a third lens (16), a fourth lens (17), a first position sensitivity detector (18) and a second position sensitivity detector (19), the transmitted light after being transmitted through the first beam splitter prism (11) is split by the second beam splitter prism (14), the transmitted light after being transmitted through the second beam splitter prism (14) reaches the Wollaston prism (15), after being split by the Wollaston prism (15), one beam of light is focused to the first position sensitivity detector (18) through the third lens (16), and the other beam of light is focused to the second position sensitivity detector (19) through the fourth lens (17), so that the focal position X of the target to be measured when it is stationary is obtained on the two position sensitivity detectors. PSD1 and Y PSD1 , and the focal position X after the angle change PSD2 and Y PSD2 After being processed by computer (23) according to the formula, the numerical output of pitch angle and yaw angle is obtained.

[0043] In a roll angle measurement system including an all-dielectric superlens array (20), a fifth lens (21) and a CCD camera (22), reflected light from a second beam splitter (14) is incident on the all-dielectric superlens array (20); the all-dielectric superlens array (20) includes a plurality of pixels, each pixel includes two different superlenses, and is capable of separating two different polarization components from an incident light beam. After passing through the fifth lens (21), the light spot is focused on the CCD camera (22), and similar to pitch angle and yaw angle measurement, the focus light spot position Z in a static state and after an angle change can be obtained respectively. PSD1 and Z PSD2 . Using the measurement principle that the pitch angle in one direction is the roll angle in the direction perpendicular to it, the CCD camera (22) can indirectly measure and calculate the change in the focal position by combining it with the all-dielectric super lens array (20), thereby obtaining the roll angle by measuring and calculating the focal position. Specifically, the CCD camera (22) receives the signal and transmits it to the computer (23), which processes it to obtain the numerical output of the roll angle. It should be noted that the front surface (receiving surface) of the CCD camera (22) needs to be perpendicular to the front surface of the measuring target mirror (10), and position calibration is required when placing it. The all-dielectric super lens array (20) is a new type of optical element based on metamaterial technology, which regulates the propagation and focusing behavior of the incident light by precisely designing the subwavelength structure (meta-atom) on the medium surface.

[0044] In summary, the first position sensitivity detector (18), the second position sensitivity detector (19) and the CCD camera (22) receive signals and transmit them to the computer (23), which then process the signals to obtain numerical outputs of the pitch angle, the yaw angle and the roll angle. The device of the present invention can achieve simultaneous high-precision measurement of small angles of three degrees of freedom.

[0045] The present invention also provides a three-degree-of-freedom angle measurement method based on radially polarized light, which is implemented based on the device of the present invention and includes the following steps:

[0046] Signals received by the first position sensitivity detector (18), the second position sensitivity detector (19) and the CCD camera (19) are transmitted to a computer (23) and processed by the computer (23) to obtain numerical outputs of pitch angle, yaw angle and roll angle.

[0047] The formula for calculating the pitch angle is:

[0048]

[0049] The calculation formula of the yaw angle is:

[0050]

[0051] In the formula, X PSD1 and Y PSD1 are respectively the focal spot positions in the horizontal and vertical directions of the first position sensitive detector (18) and the second position sensitive detector (19) in a static state; PSD2 and Y PSD2 They are respectively the focal spot positions in the horizontal and vertical directions of the first position sensitive detector (18) and the second position sensitive detector (19) after the angle change occurs; f1 and f2 are respectively the focal lengths of the third lens (16) and the fourth lens (17).

[0052] The formula for calculating the roll angle is:

[0053]

[0054] In the formula, Z PSD1 Z is the focal spot position in the vertical direction of the CCD camera (22) in a static state; PSD2 f3 is the focal spot position in the vertical direction of the CCD camera (22) after the angle change occurs; f3 is the focal length of the fifth lens (21).

[0055] In summary, the above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A three-degree-of-freedom angle measurement device based on radially polarized light, characterized in that: Including radial polarization system, polarization prism, first Wave plate, total reflection mirror, second Wave plate, SLM, measuring target mirror, first prism, wavefront detector, wavefront controller, second prism, pitch angle and yaw angle measurement system and roll angle measurement system; The radial polarization light system generates radial polarized light, which is incident on the polarization prism; The horizontal light transmitted by the polarizing prism is incident on the SLM, and after being reflected by the SLM, it reaches the measuring target mirror fixed on the target to be measured. The measuring target mirror reflects the incident light and passes through the SLM and the second The wave plate is incident on the polarizing prism, and then reflected by the polarizing prism and passes through the first After the wave plate, it reaches the total reflection mirror, and then passes through the first wave plate, then passes through the polarizing prism before entering the first prism; The vertical light reflected by the polarizing prism is incident on the first prism; The reflected light from the first prism is incident on the wavefront detector, and the wavefront information detected by the wavefront detector is fed back to the wavefront controller, and the wavefront controller generates a control signal and applies it to the SLM; The transmitted light through the first prism is incident on the second prism for spectroscopic analysis; the transmitted light through the second prism is incident on the pitch angle and yaw angle measurement system to measure the pitch angle and yaw angle; the reflected light through the second prism is incident on the roll angle measurement system to measure the roll angle.

2. The device according to claim 1, characterized in that It also includes a computer; the pitch angle and yaw angle measurement system includes a Wollaston prism, a third lens, a fourth lens, a first position sensitivity detector and a second position sensitivity detector; wherein, after being transmitted through the first beam splitter prism, the transmitted light is split through the second beam splitter prism, and the transmitted light through the second beam splitter prism reaches the Wollaston prism. After being split through the Wollaston prism, one beam of light is focused to the first position sensitivity detector through the third lens, and the other beam of light is focused to the second position sensitivity detector through the fourth lens, so that the focal position of the target to be measured when it is stationary and the focal position after the angle changes are obtained on the two position sensitivity detectors, and the numerical output of the pitch angle and the yaw angle is obtained after being calculated and processed by the computer according to the formula.

3. The device according to claim 2, characterized in that The roll angle measurement system includes an all-dielectric superlens array, a fifth lens and a CCD camera. The reflected light from the second beam splitter is incident on the all-dielectric superlens array; the all-dielectric superlens array includes multiple pixels, each pixel includes two different superlenses, which can separate two different polarization components from the incident light beam. After passing through the fifth lens, the light spot is focused on the CCD camera, and the focal spot positions in the static state and after the angle change are obtained respectively. The CCD camera is used in combination with the all-dielectric superlens array to indirectly measure and calculate the change of the focal position, thereby obtaining the roll angle by measuring and calculating the focal position. The CCD camera receives the signal and transmits it to the computer, and the computer processes it to obtain the numerical output of the roll angle.

4. The device according to claim 3, characterized in that ,The front surface of the CCD camera and the front surface of the ,measuring target mirror are perpendicular to each other, and the position ,calibration is performed when placed.

5. The device according to claim 3, characterized in that ,The all-dielectric superlens array regulates the propagation and focusing behavior of the incident light by designing the sub-wavelength structure on the ,dielectric surface.

6. The device according to any one of claims 1 to 5, characterized in that The radial polarization light system includes a laser, an S wave plate, a first lens and a second lens; the laser generates linear polarized light, which is converted into radial polarized light after passing through the S wave plate. The radial polarized light is expanded by a beam expansion system composed of a first lens and a second lens, and then incident on a polarization prism for splitting.

7. A three-degree-of-freedom angle measurement method based on radially polarized light, characterized in that: The measurement is performed using the device as claimed in any one of claims 3 to 5, comprising the following steps: The signals received by the first position sensitivity detector, the second position sensitivity detector and the CCD camera are transmitted to the computer, and are processed by the computer to obtain numerical outputs of the pitch angle, the yaw angle and the roll angle.

8. The method according to claim 7, characterized in that ,The calculation formula of the pitch angle is: The calculation formula of the yaw angle is: In the formula, X PSD1 and Y PSD1 are respectively the focal spot positions in the horizontal and vertical directions of the first position sensitive detector and the second position sensitive detector in a static state; X PSD2 and Y PSD2 are respectively the focal spot positions in the horizontal and vertical directions of the first position sensitive detector and the second position sensitive detector after the angle change occurs; f1 and f2 are respectively the focal lengths of the third lens and the fourth lens.

9. The method according to claim 7 or 8, wherein the roll angle is calculated as follows: In the formula, Z PSD1 Z is the focal spot position in the vertical direction of the CCD camera in a static state; PSD2 is the focal spot position in the vertical direction of the CCD camera after the angle change; f3 is the focal length of the fifth lens.

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