Phase scanning based optical interferometric tilt measurement apparatus and method

Abstract

A kind of optical interference type inclination measuring device and method based on phase scanning, including DC power supply, VCESL laser, laser beam vertically downward emitted by VCESL laser enters polarization beam splitter prism after collimating lens group, first laser beam and second laser beam are obtained after splitting beam through polarization beam splitter prism;First laser beam enters phase modulator in turn after passing through beam compression lens group, first mirror, the first laser beam after passing through phase modulator enters second mirror by adjusting polarization direction through 1 / 2 glass;After passing through second mirror, it is hit on frosted glass again after passing through half mirror;Second laser beam enters half mirror after passing through water surface box for detecting inclination, it is also hit on frosted glass after passing through half mirror;First laser beam and second laser beam generate interference on frosted glass;Face array CCD captures interference image generated on frosted glass, and the inclination size is inverted by data processing interference.This application greatly improves the phase resolution of interference fringe, and is convenient for realizing high-precision inclination measurement.

Description

Technical Field

[0001] This invention relates to a high-precision tilt angle measurement method, and more particularly to an optical interferometric tilt angle measurement device and method based on phase scanning. Background Technology

[0002] Existing optical tilt measurement methods mostly employ gratings or laser rangefinders, such as the published patent application "Tilting Measurement Device and Method" (patent number 202080102462.8). This patent uses two laser rangefinders to measure the position of a detection plane. By real-time compensation of the tilt angle of the detection plane, it ensures that the detection plane is always horizontal, and the tilt angle information of the carrier is derived from the compensation angle. However, due to the damping force caused by mechanical friction and limitations in the measurement accuracy of the laser rangefinders, it cannot detect tilt angle changes at the micro-radian level.

[0003] The patent application (202211647177.1) entitled "A Two-Dimensional Tilt Sensor and Tilt Measurement Method Based on Fiber Bragg Grating" proposes a tilt measurement method using fiber Bragg gratings as a displacement measurement transpose. The cantilever deforms under gravity, generating stress changes. Fiber Bragg gratings installed on both sides of the cantilever convert these stress changes into Bragg wavelength changes. The tilt angle of the carrier plane is obtained based on the Bragg wavelength changes on both sides and their correspondence with the tilt angle. However, due to the nonlinearity of cantilever deformation and stress changes, especially under large tilt angles, the nonlinear effect is particularly pronounced, making it impossible to guarantee the tilt measurement accuracy under these conditions. Furthermore, the deformation is also affected by environmental factors such as temperature, causing changes in the correspondence with stress and affecting measurement stability. Most importantly, in the scenario of measuring with a plumb bob, the absolute value of the plumb bob's reverse direction cannot be known, making it a measurement method based on relative tilt angle changes.

[0004] The most relevant patent to this invention is "High-Precision Dynamic Tilt Angle Measurement Method and Device," patent application number (202110471537.6). This patent invented a tilt angle measurement device based on liquid level sensing. It detects the liquid level difference between the two sides of a container using a liquid level sensor, and the tilt angle information of the carrier can be obtained based on the lateral distance of the sensor placement. However, the static accuracy of most liquid level sensors is generally in the range of 0.1% to 0.25%. If higher accuracy is required, more advanced sensor technologies are needed, such as millimeter-wave radar or laser rangefinders, but the improvement in accuracy is limited. This is mainly because the accuracy of liquid level sensors is also affected by various factors, such as liquid density, viscosity, temperature, pressure, and flow rate. Therefore, the ultimate accuracy and stability are insufficient for use in certain specific situations.

[0005] The aforementioned tilt angle measurement methods generally use position sensors as displacement detection methods, and obtain tilt angle values ​​based on the distance of the sensor. On the one hand, they cannot overcome the characteristics of the detection medium such as temperature, humidity and surface tension, or are limited by mechanical resistance and feedback transposition accuracy, and cannot achieve stable and high-precision tilt angle measurement. They cannot meet the requirements in situations such as long-term building settlement where the equipment needs to have long-term stability. Summary of the Invention

[0006] To overcome the above problems, the present invention provides an optical interferometric tilt measurement device and method based on phase scanning.

[0007] The first aspect of the present invention provides an optical interferometric tilt measurement device based on phase scanning, comprising a DC power supply, a VCESL laser, a collimating lens group, a beam compression lens group, a beam expanding lens group, a polarizing beam splitter prism, a pre-evacuated water surface box, a first reflecting mirror, a second reflecting mirror, a phase modulator, a half-reflecting half-lens, a half-glass slide, and a CCD array.

[0008] The VCESL laser is vertically downward. The laser beam emitted vertically downward by the VCESL laser passes through a collimating lens group and then enters a polarizing beam splitter prism. After being split by the polarizing beam splitter prism, a first laser beam and a second laser beam are obtained. The first laser beam passes through a beam compression lens group and a first reflector in sequence and then enters a phase modulator. After passing through the phase modulator, the first laser beam passes through a half-glass plate to adjust its polarization direction and then enters a second reflector. After passing through the second reflector, it passes through a semi-reflective lens and strikes a frosted glass. The path of the first laser beam is called the reference interferometer arm. The second laser beam passes through a water surface box used to detect the tilt angle and enters a semi-reflective lens. After passing through the semi-reflective lens, it also strikes a frosted glass. The path of the second laser beam is called the working interferometer arm.

[0009] The first and second laser beams interfere with each other on the frosted glass surface due to the phase difference modulated by the thickness of the liquid surface in the water box. The area CCD captures the interference image generated on the frosted glass surface. The area CCD is connected to a digital-to-analog converter (DAC) to transmit the acquired interference image to the DAC. The DAC converts the analog signal of the interference image into a digital signal and outputs it to the microprocessor. The microprocessor processes the data to retrieve the tilt angle.

[0010] Furthermore, the collimating lens group includes a beam expander and an aperture stop.

[0011] A second aspect of the present invention provides a measurement method for an optical interferometric tilt measuring device based on phase scanning, comprising the following steps:

[0012] (1) A VCESL laser emits a relatively stable laser beam, which, after passing through a polarization beam splitter, produces two linearly polarized beams S0 and S1 with perpendicular polarization directions.

[0013] (2) After passing through the beam expander and the aperture, the linearly polarized light S0 passes through a liquid of a certain depth, and after passing through the semi-reflective lens, it hits the frosted glass in front of the detector.

[0014] (3) After passing through the electro-optic phase modulator, the linearly polarized light S1 laser has an additional phase that can be adjusted between -π and π. After passing through the 1 / 2 glass plate, the reflecting cone and the half-reflecting half-lens, it hits the frosted glass in front of the detector and interferes with the laser in the S0 path. This interference information reflects the change in the thickness of the liquid on both sides of the water surface box within the range of the linearly polarized light S0 laser.

[0015] Furthermore, in step (3), the interference includes two cases:

[0016] (31) Under large tilt angle conditions, multiple periodic interference fringes were observed at the frosted glass, and the phase difference was obtained by fitting a sine function;

[0017] (32) When the tilt angle is very small, the interference fringes observed at the frosted glass can reach one-thousandth of the full period. Phase scanning is performed on the phase modulator at the path of the linearly polarized light S1. In order to improve the bandwidth, only the two positions of 0° and 90° are applied.

[0018] Furthermore, under the condition of tilt angle ε, when the phase modulator is 0 degrees, the signal strength detected by the detector on both sides is:

[0019]

[0020]

[0021] When the phase modulator is at 90 degrees, the signal strength is:

[0022]

[0023]

[0024] at this time

[0025]

[0026]

[0027] The detector performs a maximum value determination on the data collected. When no periodic fringe data exists, i.e., when the interference fringes within the detector range have not reached one period, the phase difference between the two is...

[0028]

[0029] At this point, the tilt angle can be obtained from the phase difference.

[0030]

[0031] Where d is the beam width detected by the detector, and λ is the wavelength of the laser.

[0032] The beneficial effects of this invention are:

[0033] (1) Compared with traditional tilt angle measurement methods, the tilt angle detection material used in this invention is liquid, which has no mechanical friction and no surface shape error. It adopts optical interference and has no surface contact with the liquid, thus avoiding the influence of liquid surface tension. At the same time, it adopts phase orthogonal scanning to improve the phase detection accuracy of interference fringes related to tilt angle. Under large tilt angle conditions, by judging the number of fringes at the frosted glass and combining it with the phase detection of the edge, high-precision tilt angle measurement can be achieved over a large range.

[0034] (2) Optical interference phase scanning is the main innovation of this invention. On the one hand, the laser emitted by the laser is split into two beams according to the polarization direction by a polarizing beam splitter prism. The two beams form interference along different paths. The tilt angle is measured by setting a liquid level box on the measuring interference arm. On the other hand, the method used to realize this invention is to set a phase modulator on the reference interference arm. The phase modulator is used to realize phase scanning at 0 degrees and 90 degrees, and then the minute phase change of the interference fringes is calculated to achieve high-precision tilt angle measurement.

[0035] (3) The present invention measures the tilt angle by means of optical interference, without contact with the water surface box of the sample being measured, thus avoiding system measurement errors caused by mechanical friction and liquid surface tension. At the same time, it innovatively adopts a phase scanning method, which greatly improves the phase resolution capability of the interference fringes and facilitates high-precision tilt angle measurement. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the structure of the present invention. Detailed Implementation

[0037] The technical solution of this invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0038] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are used only for the convenience of describing the invention and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0039] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0040] Example 1

[0041] See attached document Figure 1 An optical interferometric tilt measurement device based on phase scanning includes a DC power supply, a VCESL laser 1, a collimating lens group 2, a beam compression lens group 4, a beam expander lens group, a polarizing beam splitter prism, a pre-evacuated water surface box, a first reflecting mirror, a second reflecting mirror, a phase modulator, a semi-reflective mirror, a half-glass slide, a CCD array, a phase modulator driver, a microprocessor, a digital-to-analog converter, an aperture, and several mechanical mounting components.

[0042] The VCESL laser 1 is located at the top and vertically downward. Since its emitted laser has a certain divergence angle, it needs to be collimated by a collimating lens group. The laser beam emitted vertically downward by the VCESL laser 1 enters the polarization beam splitter prism 3 after passing through the collimating lens group 2. After being split by the polarization beam splitter prism 3, it becomes two linearly polarized lasers with perpendicular polarization directions, which are referred to as the first laser beam and the second laser beam, respectively, and their paths are transmission and reflection, respectively.

[0043] Because the aperture of the phase modulator is limited, the reflected light needs to be compressed by a beam compression lens group. In order to reduce the size of the instrument, the compressed light beam passes through the beam compression lens group 4 and the first reflector 5 in sequence and then enters the phase modulator 6. After passing through the phase modulator, the first laser beam passes through the 1 / 2 glass plate 7 to adjust its polarization direction and then enters the beam expander lens group 13. After beam expansion, it enters the second reflector 8. After passing through the second reflector 8, it passes through the semi-reflective mirror 9 and then hits the ground glass 10. The path of the first laser beam is called the reference interferometer arm. The second laser beam passes through the water surface box 11 used to detect the tilt angle and enters the semi-reflective mirror. After passing through the semi-reflective mirror 9, it also hits the ground glass 10. The path of the second laser beam is called the working interferometer arm.

[0044] The first and second laser beams interfere with each other on the frosted glass surface due to the phase difference modulated by the thickness of the liquid surface in the water box. The area array CCD12 captures the interference image generated on the frosted glass surface. The area array CCD12 is connected to the digital-to-analog converter (DAC) and transmits the acquired interference image to the DAC. The DAC converts the analog signal of the interference image into a digital signal and outputs it to the microprocessor. The microprocessor processes the data and inversely calculates the tilt angle.

[0045] The collimating lens group includes a beam expander and an aperture stop.

[0046] Example 2

[0047] A measurement method for an optical interferometric tilt measuring device based on phase scanning includes the following steps:

[0048] (1) A VCESL laser emits a relatively stable laser beam, which, after passing through a polarization beam splitter, produces two linearly polarized beams S0 and S1 with perpendicular polarization directions.

[0049] (2) After passing through the beam expander and the aperture, the linearly polarized light S0 passes through a liquid of a certain depth, and after passing through the semi-reflective lens, it hits the frosted glass in front of the detector.

[0050] (3) After passing through the electro-optic phase modulator, the linearly polarized light S1 laser has an additional phase that can be adjusted between -π and π. After passing through the 1 / 2 glass plate, the reflecting cone and the half-reflecting half-lens, it hits the frosted glass in front of the detector and interferes with the laser in the S0 path. This interference information reflects the change in the thickness of the liquid on both sides of the water surface box within the range of the linearly polarized light S0 laser.

[0051] In step (3), the interference includes two cases:

[0052] (31) Under large tilt angle conditions, multiple periodic interference fringes were observed at the frosted glass, and the phase difference was obtained by fitting a sine function;

[0053] (32) When the tilt angle is very small, the interference fringes observed at the frosted glass reach one-thousandth of the full period. Phase scanning is performed on the phase modulator at the path of the linearly polarized light S1. In order to increase the bandwidth, only the two positions of 0° and 90° are applied.

[0054] Example 3

[0055] Based on Example 2, under the condition of tilt angle ε, when the phase modulator is 0 degrees, the signal strength detected by the detector on both sides is:

[0056]

[0057]

[0058] When the phase modulator is at 90 degrees, the signal strength is:

[0059]

[0060]

[0061] at this time

[0062]

[0063]

[0064] The detector performs a maximum value determination on the data collected. When no periodic fringe data exists, i.e., when the interference fringes within the detector range have not reached one period, the phase difference between the two is...

[0065]

[0066] At this point, the tilt angle can be obtained from the phase difference.

[0067]

[0068] Where d is the beam width detected by the detector, and λ is the wavelength of the laser.

[0069] The embodiments described in this specification are merely examples of implementations of the inventive concept. The scope of protection of this invention should not be considered as limited to the specific forms stated in the embodiments. The scope of protection of this invention also extends to equivalent technical means that can be conceived by those skilled in the art based on the inventive concept.

Claims

1. A phase scanning based optical interferometric tilt measurement apparatus, characterized by: Includes DC power supply, VCESL laser, collimating lens group, beam compression lens group, beam expanding lens group, polarizing beam splitter prism, pre-evacuated water surface box, first reflecting mirror, second reflecting mirror, phase modulator, half-reflecting half-lens, half-glass slide, and area CCD array; The VCESL laser is set vertically downward. The laser beam emitted vertically downward by the VCESL laser enters the polarization beam splitter after passing through the collimating lens group. After being split by the polarization beam splitter, a first laser beam and a second laser beam are obtained. The first laser beam passes through the beam compression lens group and the first reflector in sequence and then enters the phase modulator. After passing through the phase modulator, the first laser beam is adjusted in polarization direction by a 1 / 2 glass plate and then enters the second reflector. After passing through the second reflector and then through the semi-reflective lens, the first laser beam strikes the frosted glass. The path of the first laser beam is called the reference interferometer arm. The second laser beam passes through the water surface box used to detect the tilt angle, enters the semi-reflective lens, and after passing through the semi-reflective lens, also strikes the frosted glass. The path of the second laser beam is called the working interferometer arm. The first laser beam and the second laser beam are affected by the phase difference modulated by the thickness of the liquid surface in the water box, and the first laser beam and the second laser beam interfere on the frosted glass. The area array CCD captures the interference image generated on the frosted glass. The area array CCD is connected to the digital-to-analog converter and transmits the acquired interference image to the digital-to-analog converter. The digital-to-analog converter converts the analog signal of the dry image into a digital signal and outputs it to the microprocessor. The microprocessor then processes the data to determine the tilt angle.

2. A phase scanning based optical interferometric tilt measurement apparatus as claimed in claim 1, characterized in that: The collimating lens group includes a beam expander and an aperture stop.

3. A measurement method based on the phase-scanning-based optical interferometric tilt measuring device according to claim 2, characterized in that, Includes the following steps: (1) A VCESL laser emits a relatively stable laser beam, which, after passing through a polarization beam splitter, produces two linearly polarized beams S0 and S1 with perpendicular polarization directions. (2) After passing through the beam expander and the aperture, the linearly polarized light S0 passes through a liquid of a certain depth, and after passing through the semi-reflective lens, it hits the frosted glass in front of the detector. (3) After passing through the electro-optic phase modulator, the linearly polarized light S1 laser has an additional phase that can be adjusted between -π and π. After passing through the 1 / 2 glass plate, the reflecting cone and the half-reflecting half-lens, it also hits the frosted glass in front of the detector and interferes with the laser in the S0 path. This interference information reflects the change in the thickness of the liquid on both sides of the water box within the range of the linearly polarized light S0 laser.

4. The measurement method as described in claim 3, characterized in that, In step (3), the interference includes two cases: (31) Under large tilt angle conditions, multiple periodic interference fringes were observed at the frosted glass, and the phase difference was obtained by fitting a sine function; (32) When the tilt angle is very small, the interference fringes observed at the frosted glass can reach one-thousandth of the full period. Phase scanning is performed on the phase modulator at the path of the linearly polarized light S1. In order to increase the bandwidth, only the two positions of 0° and 90° are applied.

5. The measurement method as described in claim 4, characterized in that: Under the condition of tilt angle ε, when the phase modulator is 0 degrees, the signal strength detected by the detector on both sides is: When the phase modulator is at 90 degrees, the signal strength is: at this time The detector performs a maximum value determination on the data collected. When no periodic fringe data exists, i.e., when the interference fringes within the detector range have not reached one period, the phase difference between the two is... At this point, the tilt angle can be obtained from the phase difference. Where d is the beam width detected by the detector, and λ is the wavelength of the laser.

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