A single-beam three-degree-of-freedom pose measurement method and device based on heterodyne interference and autocollimation

Abstract

This invention belongs to the field of three-degree-of-freedom pose measurement technology, and relates to a single-beam three-degree-of-freedom pose measurement method and device based on heterodyne interferometry and self-collimation. The measurement method includes the following steps: Step 1: A laser beam is split into two beams with a certain frequency difference; Step 2: In the self-collimation module, the laser is split into a first reference beam and a first beam; the first beam is modulated, reflected, and then modulated again to split into a first measurement beam and a second beam; the second beam is modulated to a first photoelectric detection module; Step 3: In the heterodyne interferometry optical path, the laser is split into a second reference beam and a third beam; the third beam is modulated, reflected, and then split into a second measurement beam and a fourth beam; the two reference beams are merged to form a first interference beam, and the two measurement beams are merged to form a second interference beam; Step 4: A circuit module acquires the angle and displacement; The measurement device includes an optomechanical module, a target under test, and a circuit module. Using the above scheme, displacement and angle are measured simultaneously.

Description

Technical Field

[0001] This invention belongs to the field of three-degree-of-freedom pose measurement technology, specifically relating to a single-beam three-degree-of-freedom pose measurement method and device based on heterodyne interference and self-collimation. Background Technology

[0002] In the manufacturing process of high-end equipment, ultra-precision positioning ensures processing quality and manufacturing accuracy through precise measurement of angles and poses. Three-degree-of-freedom pose measurement is a key method in ultra-precision positioning. Taking a grating ruling machine as an example, the accompanying angular runout caused by the straightness of the motion stage guide rail will cause errors in displacement measurement, which in turn will cause deviations in the motion of the motion stage, resulting in deviations in the straightness of the grating lines. Only by simultaneously measuring the accompanying angle values ​​can the deviations be accurately compensated. Therefore, a three-degree-of-freedom pose measurement method is needed to simultaneously measure the runout angles around two coordinate axes orthogonal to the displacement direction and perpendicular to each other while measuring the linear displacement.

[0003] Currently, in the field of three-degree-of-freedom measurement of linear displacement and yaw angle, existing solutions have certain problems, and the patent portfolio is not yet mature: For example, SIOS' SP-5000 TR model uses a multi-beam differential interferometer method. It obtains the yaw angle value by calculating the difference between the readings of two parallel laser interferometers with a known spacing, based on trigonometric geometric relationships. However, this method also has the following shortcomings: First, the interferometer is an incremental measurement instrument and cannot measure absolute angles and attitudes; second, the interferometer spacing is related to mechanical adjustment and structural stability, making it difficult to measure accurately; and third, achieving two-dimensional angle measurement requires differential measurement of three laser interferometers, which is bulky, complex in structure, and expensive.

[0004] For example, patent document CN112857207A published by Yu Liang et al. of Harbin Institute of Technology discloses a single-beam three-degree-of-freedom zero-difference laser interferometer based on an array detector. It acquires interferograms using an image sensor and performs fringe analysis to calculate the two-dimensional yaw angle, thus achieving three-degree-of-freedom measurement. However, the differential wavefront imaging method suffers from slow speed, low sampling rate, and large data volume, making it difficult to meet the requirements of high-speed, real-time measurement.

[0005] For example, the international patent US20050157310A1 published by Kim Jae-wan et al. of the Korea National Institute of Standards and Technology discloses a three-degree-of-freedom measurement method combining autocollimation and zero-difference interferometry. This method uses autocollimation to measure the two-dimensional yaw angle and zero-difference interferometry to measure linear displacement. However, compared with heterodyne interferometry, zero-difference interferometry has drawbacks such as poor dynamic performance and poor resistance to environmental interference, limiting its application in high-end equipment nano-positioning scenarios.

[0006] The above research indicates that, currently, the field of three-degree-of-freedom pose measurement still lacks a measurement method and device that combines high speed, high resolution, and an absolute angular zero point. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a single-beam three-degree-of-freedom pose measurement method and apparatus based on heterodyne interference and self-collimation, which simultaneously measures the linear displacement of the target in the beam propagation direction and the yaw angle around two coordinate axes orthogonal to the beam propagation direction and perpendicular to each other.

[0008] This invention provides a single-beam three-degree-of-freedom pose measurement method based on heterodyne interferometry and self-collimation, comprising the following steps: Step 1: A beam of light with a fixed frequency is emitted by a single-frequency laser. After being modulated by a modulator, it is split into two beams with a certain frequency difference and stable phase difference by a beam splitter. The beams include a first laser beam and a second laser beam. The first laser beam enters the self-collimation module, and the second laser beam enters the heterodyne interference module. Step 2: In the self-collimation module, the first laser beam enters the optical path of the heterodyne interferometer after passing through the first beam splitting module, the first lens group module, and the first polarization control module. The first laser beam is split into the first reference beam and the first beam by the second beam splitting module according to the polarization state. The first beam passes through the third beam splitting module and the second polarization control module in sequence and is incident on the first reflective target. After reflection, it passes through the second polarization control module and is split into the first measurement beam and the second beam by the third beam splitting module according to the polarization state. The second beam returns to the self-collimating optical path, passes through the second beam splitting module, the first polarization control module, and the first lens group module, and is reflected at the first beam splitting module to the first photoelectric detection module. Step 3: In the optical path of the heterodyne interferometer, the second laser beam passes through the collimation module, and the collimated light is split into the second reference beam and the third beam according to the polarization state in the second beam splitting module. The third beam then passes through the third beam splitting module and the third polarization control module and is incident on the second reflection target. After reflection, it passes through the third beam splitting module and is split into the second measurement beam and the fourth beam according to the polarization state. The first reference beam and the second reference beam merge to form the first interference beam and are incident on the surface of the second photoelectric detection module. The first measurement beam and the second measurement beam merge to form the second interference beam and are incident on the surface of the third photoelectric detection module. The two interference beams each generate optical beat frequency interference. Step 4: Obtain the yaw angle and linear displacement through the circuit module; Furthermore, in the circuit module, the signal processing board connects the first photoelectric detection module, the second photoelectric detection module, and the third photoelectric detection module. By demodulating the information from the first photoelectric detection module, the yaw angle of the reflective target around two coordinate axes that are orthogonal to the beam propagation direction and mutually perpendicular is obtained. Furthermore, in the circuit module, the signal processing board connects the first photoelectric detection module, the second photoelectric detection module, and the third photoelectric detection module. By demodulating the information from the second and third photoelectric detection modules, the linear displacement of the reflective target perpendicular to the optical axis is obtained.

[0009] Furthermore, in the circuit module, for information from the first photoelectric detection module, the zero-position (using the initial spot position of the system as the zero position) of the spot (x0, y0) is recorded. When the object being measured deflects, the current spot position (X, Y) is obtained; from geometric relationships, θx = K (Y - y0), θy = K (X - x0) where K is a coefficient related to the focal length, the optical plate position sensor, and the signal processing board. For information from the second and third photoelectric detection modules, the phase difference Δ between the two signals is used. (t) yields the displacement of the target along the optical axis: L(t) = Δ (t)λ / 4π, the linear displacement of the target under test in the direction of beam propagation can be obtained by the signal processing board.

[0010] The present invention also provides a single-beam three-degree-of-freedom pose measurement device based on heterodyne interferometry and self-collimation, including an optomechanical module, a target under test, and a circuit module. The target under test is located at the beam emission end of the optomechanical module, and the circuit module is located at the beam emission end of the optomechanical module.

[0011] Furthermore, the optomechanical module includes a heterodyne laser source module, a self-collimation module, and a heterodyne interference module; the heterodyne laser source module emits two beams, including a first beam and a second beam, wherein the first beam is incident on the self-collimation module and the second beam is incident on the heterodyne interference module.

[0012] Furthermore, the heterodyne laser source module includes a single-frequency laser, an optical isolator, a beam splitter, a first modulator, a second modulator, a first single-mode polarization-maintaining fiber, a second single-mode polarization-maintaining fiber, a first fiber coupler, and a second fiber coupler. The laser output of the single-frequency laser is connected to the optical isolator, the output of the optical isolator is connected to the beam splitter, the beam splitter is connected to the first modulator and the second modulator, and the first modulator and the second modulator are respectively connected to the first single-mode polarization-maintaining fiber and the second single-mode polarization-maintaining fiber.

[0013] Furthermore, the self-collimation module includes a first polarizing beam splitter, a first collimating objective lens group, and a first quarter-wave plate with an optical axis of 45°. The first polarizing beam splitter is formed by cementing two right-angled prisms together. The four right-angled faces of the two right-angled prisms are respectively the first working surface, the second working surface, the third working surface, and the fourth working surface of the first polarizing beam splitter. The cemented surface of the two right-angled prisms is the polarizing beam splitting surface of the first polarizing beam splitter. The first quarter-wave plate with an optical axis of 45° is disposed on the second beam splitting surface of the first polarizing beam splitter. The incident beam enters through the first beam splitting surface, and the second working surface is located on the opposite side of the first working surface. The first collimating objective lens group is disposed between the first quarter-wave plate with an optical axis of 45° and the second beam splitting surface of the first polarizing beam splitter.

[0014] Furthermore, the heterodyne interference module includes a second collimating objective lens group, a second polarizing beam splitter, a third polarizing beam splitter, a second quarter-wave plate with an optical axis of 22.5°, a third quarter-wave plate with an optical axis of 45°, a first polarizer, a second polarizer, and a reference mirror. The second polarizing beam splitter is formed by cementing two right-angle prisms together, and the four right-angle faces of the two right-angle prisms are respectively the first working surface, the second working surface, the third working surface, and the fourth working surface of the second polarizing beam splitter. The third polarizing beam splitter is also formed by cementing two right-angle prisms together, and the four right-angle faces of the two right-angle prisms are respectively the first working surface, the second working surface, the third working surface, and the fourth working surface of the first polarizing beam splitter. The incident beam enters through the first beam-splitting surface of the second polarizing beam splitter; the second working surface of the second polarizing beam splitter is located on the opposite side of the first working surface, and the first working surface of the third polarizing beam splitter is behind the second beam-splitting surface of the second polarizing beam splitter; the second collimating objective lens group is located behind the third working surface of the second polarizing beam splitter; the first polarizer is located behind the fourth working surface of the second polarizing beam splitter. The second working surface of the third polarizing beam splitter is located on the opposite side of the first working surface, the second quarter-wave plate with an optical axis of 22.5° is located behind the second working surface of the third polarizing beam splitter, the third quarter-wave plate with an optical axis of 45° is located behind the third working surface of the third polarizing beam splitter, the reference mirror is located behind the third quarter-wave plate with an optical axis of 45°, and the second polarizer is located behind the fourth working surface of the third polarizing beam splitter.

[0015] Furthermore, the circuit module includes a photoelectric detection module and a signal processing board, with the photoelectric detection module connected to the signal processing board via wires.

[0016] Furthermore, the photoelectric detection module includes a first converging collimator, a second converging collimator, a spot position sensor, a first photodetector, and a second photodetector. For the self-collimation module, its spot position sensor is disposed on the third beam-splitting surface of the first polarizing beam splitter and is located at the focal plane of the reflected light, used to receive the reflected light and obtain the yaw angle of the object around two coordinate axes orthogonal to the beam propagation direction and mutually perpendicular. For the heterodyne interference module, the first photodetector is disposed on the focal plane of the first converging collimator, and the second photodetector is disposed on the focal plane of the second converging collimator. The first photodetector is disposed behind the first polarizer, and the second photodetector is disposed behind the second polarizer.

[0017] Furthermore, the signal processing board is connected to the spot position sensor, the first photodetector, and the second photodetector via wires.

[0018] Furthermore, the first collimating objective lens group is divided into multiple objective lenses, including a collimating lens group, a front lens group, a first rear lens group, and a second rear lens group; wherein, the collimating lens group is located on the first working surface of the first polarizing beam splitter, the front lens group is located between the first working surface of the first polarizing beam splitter and the collimating lens group, the first rear lens group is located on the second working surface of the first polarizing beam splitter, and the second rear lens group is located on the third working surface of the first polarizing beam splitter; wherein the collimating lens group is used to collimate the first incident beam, the front lens group is used to expand the beam, the first rear lens group is used to collimate the beam, and the first and second rear lens groups are used to converge the beam.

[0019] Beneficial effects This invention integrates the principles of autocollimation and heterodyne interferometry. By processing information obtained from a spot position sensor, it enables simultaneous measurement of the relative displacement of a target along the optical axis and absolute measurement of two-axis rotation angles using a single beam. Compared to traditional differential interferometry schemes, this invention eliminates the need for additional machine parameters (such as interferometer spacing), simplifies mechanical assembly and adjustment, improves structural stability, and offers a simpler structure, easier miniaturization, and lower cost.

[0020] Compared with the single-beam three-degree-of-freedom measurement scheme based on image sensor acquisition of interferometric wavefront images, the scheme of the present invention utilizes the self-collimator measurement principle and measures the two-dimensional yaw angle through PSD, which has the advantages of high speed and high sampling rate, and can meet the needs of high-speed and real-time measurement.

[0021] Compared with the three-degree-of-freedom measurement method based on the combination of autocollimation and zero-difference interferometer, the present invention uses the autocollimator measurement optical path and the heterodyne interferometer optical path to fuse, which retains the advantages of heterodyne interferometry in terms of better dynamic performance and stronger resistance to environmental interference.

[0022] In summary, compared with the prior art, the advantages of this invention are that it combines high speed, high resolution, and an absolute angular zero point. Attached Figure Description

[0023] Appendix Figure 1 This is a schematic diagram of a laser source module in a single-beam three-degree-of-freedom pose measurement device based on heterodyne interferometry and self-collimation.

[0024] Appendix Figure 2 This is a schematic diagram of a single-beam three-degree-of-freedom pose measurement device based on heterodyne interferometry and self-collimation.

[0025] Appendix Figure 3 This is a schematic diagram of a single-beam three-degree-of-freedom pose measurement device based on heterodyne interference and self-collimation, in which the first collimating objective lens group is divided into a collimating lens group, a front lens group, a first rear lens group, and a second rear lens group.

[0026] Figure reference numerals: 1 Optomechanical module; 2 Target under test; 3 Circuit module; 11 Heterodyne laser source module; 12 Self-collimation module; 13 Heterodyne interferometry module; 31 Photoelectric detection module; 32 Signal processing board; 111 Single-frequency laser; 112 Optical isolator; 113 Beam splitter; 114a First modulator; 114b Second modulator; 115a First single-mode polarization-maintaining fiber; 115b Second single-mode polarization-maintaining fiber; 116a First fiber coupler; 116b Second fiber coupler; 121 First polarization beam splitter prism; 122 First collimating objective lens group; 12 3. First quarter-wave plate with an optical axis of 45°; 131. Second collimating objective lens group; 132a. Second polarizing beam splitter; 132b. Third polarizing beam splitter; 133a. Second quarter-wave plate with an optical axis of 22.5°; 133b. Third quarter-wave plate with an optical axis of 45°; 134a. First polarizer; 134b. Second polarizer; 135. Reference mirror; 311a. First converging collimator; 311b. Second converging collimator; 312. Spot position sensor; 313a. First photodetector; 313b. Second photodetector. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] First Embodiment Please refer to Figures 1-3 It includes an optomechanical module 1, a target under test 2, and a circuit module 3; Optomechanical module 1 includes a heterodyne laser source module 11, a self-collimation module 12, and a heterodyne interference module 13; The heterodyne laser source module includes a single-frequency laser 111, an optical isolator 112, a beam splitter 113, a first modulator 114a, a second modulator 114b, a first single-mode polarization-maintaining fiber 115a, a second single-mode polarization-maintaining fiber 115b, a first fiber coupler 116a, and a second fiber coupler 116b. The single-frequency laser 111 emits a single-frequency laser beam, which is split into two laser beams by the optical isolator 112 and the beam splitter 113, referred to as the first incident beam and the second incident beam. The first incident beam passes through the first modulator 114a, the first single-mode polarization-maintaining fiber 115a, and the first fiber coupler 116a, while the second incident beam passes through the second modulator 114b, the second single-mode polarization-maintaining fiber 116b, and the second fiber coupler 115b before being incident on the back-end system. The optical isolator 112 is used to prevent the backlight from affecting the heterodyne laser source module 11.

[0029] The autocollimation module 12 includes a first polarizing beam splitter 121, a first collimating objective lens group 122, and a first quarter-wave plate 123 with an optical axis of 45°. The first polarizing beam splitter 121 is formed by cementing two right-angled prisms together. The four right-angled faces of the two prisms are respectively the first working surface, second working surface, third working surface, and fourth working surface of the first polarizing beam splitter 121. The cemented surface of the two right-angled prisms is the polarizing beam splitting surface of the first polarizing beam splitter 121. The first quarter-wave plate 123 with an optical axis of 45° is disposed on the second beam splitting surface of the first polarizing beam splitter 121. The incident beam enters through the first beam splitting surface, and the second working surface is located on the opposite side of the first working surface. The first collimating objective lens group 122 is disposed between the first quarter-wave plate 123 with an optical axis of 45° and the second beam splitting surface of the first polarizing beam splitter 121.

[0030] The first collimating objective lens group 122 includes a collimating lens group 122a, a front lens group 122b, a first rear lens group 112c, and a second rear lens group 122d. The first incident beam 51a is modulated into collimated light by 122a and emitted. After being expanded by 122b and 122c, it is emitted into the first quarter-wave plate 123 with an optical axis direction of 45°. The second beam 53b is emitted into the reflecting surface of the first polarizing beam splitter 121 after passing through 122c. After being converged by 122d, it is emitted into the spot position sensor 32.

[0031] The heterodyne interference module 13 includes a second collimating objective lens group 131, a second polarizing beam splitter 132a, a third polarizing beam splitter 132b, a second quarter-wave plate 133a with an optical axis of 22.5°, a third quarter-wave plate 133b with an optical axis of 45°, a first polarizer 134a, a second polarizer 134b, and a reference mirror 135. The second polarizing beam splitter 132a is formed by cementing two right-angle prisms together, and the four right-angle faces of the two right-angle prisms are respectively the first working surface, the second working surface, the third working surface, and the fourth working surface of the second polarizing beam splitter 132a. The third polarizing beam splitter 133a is also formed by cementing two right-angle prisms together, and the four right-angle faces of the two right-angle prisms are respectively the first working surface, the second working surface, the third working surface, and the fourth working surface of the first polarizing beam splitter 133a. The incident beam enters through the first beam-splitting surface of the second polarizing beam splitter 132a; the second working surface of the second polarizing beam splitter 132a is located on the opposite side of the first working surface; the first working surface of the third polarizing beam splitter 133a is behind the second beam-splitting surface of the second polarizing beam splitter 132a; the second collimating objective lens group 131 is located behind the third working surface of the second polarizing beam splitter 132a; and the first polarizer 134a is located behind the fourth working surface of the second polarizing beam splitter 132a. The second working surface of the third polarizing beam splitter 133a is located on the opposite side of the first working surface. The second quarter-wave plate 133a with an optical axis direction of 22.5° is located behind the second working surface of the third polarizing beam splitter 133a. The third quarter-wave plate 133b with an optical axis direction of 45° is located behind the third working surface of the third polarizing beam splitter 133a. The reference mirror 135 is located behind the third quarter-wave plate 133b with an optical axis direction of 45°. The second polarizer 134b is located behind the fourth working surface of the third polarizing beam splitter 132a.

[0032] The target 2 is located behind the second quarter-wave plate 133a with an optical axis of 22.5°. Circuit module 3 includes a photoelectric detection module 31 and a signal processing board 32; The photoelectric detection module 31 includes a first converging collimator 311a, a second converging collimator 311b, a spot position sensor 312, a first photodetector 313a, and a second photodetector 313b. For the self-collimation module 12, its spot position sensor 312 is disposed on the third beam-splitting surface of the first polarizing beam splitter 121 and is located at the focal plane of the reflected light. It is used to receive the reflected light and obtain the yaw angle of the object around two coordinate axes that are orthogonal to the beam propagation direction and mutually perpendicular. For the heterodyne interference module 13, the first photodetector 313a is disposed on the focal plane of the first converging collimator 311a, and the second photodetector 313b is disposed on the focal plane of the second converging collimator 311b. The first photodetector 313a is disposed behind the first polarizer 134a, and the second photodetector 313b is disposed behind the second polarizer 134b.

[0033] The signal processing board 32 is connected to the spot position sensor 312, the first photodetector 313a, and the second photodetector 313b via wires.

[0034] Second Embodiment This embodiment provides a single-beam three-degree-of-freedom pose measurement method based on heterodyne interferometry and self-collimation, which is based on a single-beam three-degree-of-freedom pose measurement device based on heterodyne interferometry and self-collimation in the first embodiment.

[0035] The method includes the following steps: Step 1: A spatial beam with a fixed frequency is emitted by a single-frequency laser 111. After being modulated by a beam splitter 113, it is split into two beams. These beams are then converted into beams with a certain frequency difference and stable phase difference by a first modulator 114a and a second modulator 114b, respectively. The frequencies of the two beams are f1 and f2, respectively. They are then incident on the rear system through a first single-mode polarization-maintaining fiber 115a, a first fiber coupler 116a, a second single-mode polarization-maintaining fiber 115b, and a second fiber coupler 116b, respectively. The beams with frequencies f1 and f2 are the first incident beam 41a and the second incident beam 41b, respectively, and enter the self-collimation module 12 and the heterodyne interference module 13, respectively.

[0036] Step two: The first incident beam 41a is collimated by the first collimating objective lens group 122 after passing through the first polarizing beam splitter 121. After passing through the first quarter-wave plate 123 with an optical axis of 45°, its polarization state changes. The first incident beam 41a is then incident on the heterodyne interference module 13 and split into the first reference beam 42a and the first beam 43a according to their polarization states at the second polarizing beam splitter 132a. The first beam 43a passes through the third polarizing beam splitter 132b and its polarization state changes at the second quarter-wave plate 133a with an optical axis of 22.5°. The beam changes direction and exits the heterodyne interferometer module 13; after hitting the target 2 and being reflected, it re-enters the heterodyne interferometer module 13. After passing through the second quarter-wave plate 133a with an optical axis of 22.5°, it is split into a first measurement beam 44a and a second beam 43b according to the polarization state at the third polarization beam splitter 132b. The second beam 43b then passes through the second polarization beam splitter 132a, the first quarter-wave plate 123 with an optical axis of 45°, and the first collimating objective lens group 122, and is reflected at the first polarization beam splitter 121. After converging, it hits the spot position sensor 312. Step 3: The incident beam 41b is incident on the heterodyne interference module 13 and modulated into collimated light by the second collimating objective lens group 131. At the second polarizing beam splitter 132a, it is split into a second reference beam 42b and a third beam 43c according to the polarization state. After being reflected by the third polarizing beam splitter 132b, the third beam 43c is incident on the third quarter-wave plate 133b with an optical axis direction of 45°. It is then reflected by the reference mirror and passes through the third quarter-wave plate 133b with an optical axis direction of 45° again. At the third polarizing beam splitter 132b, it is split into a second measurement beam 44b and a fourth beam 43d according to the polarization state. The fourth beam 43d is reflected at the second polarizing beam splitter 132a. The first reference beam 42a and the second reference beam 42b pass through the first polarizer 134a, are incident on the first converging collimator 311a, and then converge to the first photodetector 313a to form an interference beam; the first measurement beam 54a and the second measurement beam 44b pass through the second polarizer 134b, are incident on the second converging collimator 311b, and then converge to the second photodetector 313b to form an interference beam.

[0037] Step four: The spot position sensor 312 acquires autocollimation information and records the spot position (x0, y0) at the zero point (using the initial spot position of the system as the zero point). When the object being measured deflects, the current spot position (X, Y) is obtained; from geometric relationships, θx = K (Y - y0), θy = K (X - x0), where K is a coefficient related to the focal length, the position sensor 312, and the signal processing board 32. The signal processing board 32 can obtain the yaw angle of the target 2 around two coordinate axes orthogonal to the displacement direction and perpendicular to each other. The first photodetector 313a and the second photodetector 313b acquire heterodyne interference information, forming a heterodyne interference measurement. By solving the Doppler frequency shift signal, the phase difference Δ between the two signals is obtained. (t) yields the displacement of the target along the optical axis: L(t) = Δ (t)λ / 4π, the linear displacement of the target 2 in the beam propagation direction can be obtained by signal processing board 32.

[0038] It can obtain the yaw angle of the target 2 around two coordinate axes that are orthogonal to the displacement direction and perpendicular to each other, as well as the linear displacement in the beam propagation direction.

[0039] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," "outer," "front," and "rear," etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description, and 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 a limitation of 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.

[0040] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" 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 communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances. Without conflict, the embodiments and features in the embodiments of this invention can be combined with each other.

[0041] The embodiments described above are merely illustrative of implementation methods of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A single-beam three-degree-of-freedom measurement method based on heterodyne interferometry and self-collimation, characterized in that, Includes the following steps: Step 1: A beam of light with a fixed frequency is emitted by a single-frequency laser. After being modulated by a modulator, it is split into two beams with a certain frequency difference and stable phase difference by a beam splitter. The beams include a first laser beam and a second laser beam. The first laser beam enters the self-collimation module, and the second laser beam enters the heterodyne interference module. Step 2: In the self-collimation module, the first laser beam enters the optical path of the heterodyne interferometer after passing through the first beam splitting module, the first lens group module, and the first polarization control module. The first laser beam is split into the first reference beam and the first beam by the second beam splitting module according to the polarization state. The first beam passes through the third beam splitting module and the second polarization control module in sequence and is incident on the first reflective target. After reflection, it passes through the second polarization control module and is split into the first measurement beam and the second beam by the third beam splitting module according to the polarization state. The second beam returns to the self-collimating optical path, passes through the second beam splitting module, the first polarization control module, and the first lens group module, and is reflected at the first beam splitting module to the first photoelectric detection module. Step 3: In the optical path of the heterodyne interferometer, the second laser beam passes through the collimation module, and the collimated light is split into the second reference beam and the third beam according to the polarization state in the second beam splitting module. The third beam then passes through the third beam splitting module and the third polarization control module and is incident on the second reflection target. After reflection, it passes through the third beam splitting module and is split into the second measurement beam and the fourth beam according to the polarization state. The first reference beam and the second reference beam merge to form the first interference beam and are incident on the surface of the second photoelectric detection module. The first measurement beam and the second measurement beam merge to form the second interference beam and are incident on the surface of the third photoelectric detection module. The two interference beams each generate optical beat frequency interference. Step 4: Obtain the yaw angle and linear displacement through the circuit module.

2. The single-beam three-degree-of-freedom measurement method based on heterodyne interferometry and self-collimation according to claim 1, characterized in that, In the circuit module, the signal processing board connects the first photoelectric detection module, the second photoelectric detection module, and the third photoelectric detection module. By demodulating the information from the first photoelectric detection module, the deflection angle of the reflective target around two coordinate axes that are orthogonal to the beam propagation direction and perpendicular to each other is obtained.

3. The single-beam three-degree-of-freedom measurement method based on heterodyne interferometry and self-collimation according to claim 1, characterized in that, In the circuit module, the signal processing board connects the first photoelectric detection module, the second photoelectric detection module, and the third photoelectric detection module. By demodulating the information from the second and third photoelectric detection modules, the linear displacement of the reflective target perpendicular to the optical axis is obtained.

4. The single-beam three-degree-of-freedom measurement method based on heterodyne interferometry and self-collimation according to claim 1, characterized in that, In the circuit module, for information from the first photoelectric detection module, the zero-position light spot position (x0, y0) is recorded; when the measured object deflects, the current light spot position (X, Y) is obtained; from geometric relationships, θx = K (Y - y0), θy = K (X - x0) where K is a coefficient related to the focal length, the optical plate position sensor, and the signal processing board. For information from the second and third photoelectric detection modules, the phase difference Δ between the two signals is used. (t) yields the displacement of the target along the optical axis: L(t) = Δ (t)λ / 4π, the linear displacement of the target under test in the direction of beam propagation can be obtained by the signal processing board.

5. A single-beam three-degree-of-freedom measurement device based on heterodyne interference and self-collimation, comprising an optomechanical module (1), a target under test (2), and a circuit module (3), wherein the optomechanical module (1) is provided with multiple beam emission ends, and the target under test (2) and the circuit module (3) are provided with different beam emission ends.

6. A single-beam three-degree-of-freedom measurement device based on heterodyne interferometry and self-collimation according to claim 5, characterized in that, The optomechanical module (1) includes a heterodyne laser source module (11), a self-collimation module (12), and a heterodyne interference module (13). The heterodyne laser source module (11) emits two beams, including a first beam and a second beam, wherein the first beam is incident on the self-collimation module (12) and the second beam is incident on the heterodyne interference module (13).

7. A single-beam three-degree-of-freedom measurement device based on heterodyne interferometry and self-collimation according to claim 6, characterized in that, The heterodyne laser source module (11) includes a single-frequency laser (111), an optical isolator (112), a beam splitter (113), a first modulator (114a), a second modulator (114b), a first single-mode polarization-maintaining fiber (115a), a second single-mode polarization-maintaining fiber (115b), a first fiber coupler (116a), and a second fiber coupler (116b). The laser output of the single-frequency laser (111) is connected to the optical isolator (112), the output of the optical isolator (112) is connected to the beam splitter (113), the beam splitter (113) is connected to the first modulator (114a) and the second modulator (114b), the first modulator (114a) is connected to the first single-mode polarization-maintaining fiber (115a), and the second modulator (114b) is connected to the second single-mode polarization-maintaining fiber (115b).

8. A single-beam three-degree-of-freedom measurement device based on heterodyne interferometry and self-collimation according to claim 6, characterized in that, The self-collimation module (12) includes a first polarizing beam splitter (121), a first collimating objective lens group (122), and a first quarter-wave plate (123) with an optical axis direction of 45°. The first polarizing beam splitter (121) is formed by bonding two right-angled prisms together. The four right-angled surfaces of the two right-angled prisms are the first working surface, the second working surface, the third working surface, and the fourth working surface of the first polarizing beam splitter (121), respectively. The bonding surface of the two right-angled prisms is the polarizing beam splitting surface of the first polarizing beam splitter (121). The first quarter-wave plate (123) with an optical axis direction of 45° is set on the second beam splitting surface of the first polarizing beam splitter (121). The incident beam enters from the first beam splitting surface. The second working surface is located on the opposite side of the first working surface. The first collimating objective lens group (122) is set between the first quarter-wave plate (123) with an optical axis direction of 45° and the second beam splitting surface of the first polarizing beam splitter (121).

9. A single-beam three-degree-of-freedom measurement device based on heterodyne interferometry and self-collimation according to claim 6, characterized in that, The heterodyne interference module (13) includes a second collimating objective lens group (131), a second polarizing beam splitter (132a), a third polarizing beam splitter (132b), a second quarter-wave plate (133a) with an optical axis of 22.5°, a third quarter-wave plate (133b) with an optical axis of 45°, a first polarizer (134a), a second polarizer (134b), and a reference mirror (135). The second polarizing beam splitter (132a) is formed by cementing two right-angle prisms together. The four right-angled faces of the prism are the fifth, sixth, seventh, and eighth working faces of the second polarizing beam splitter (132a), respectively; the third polarizing beam splitter (133a) is formed by cementing two right-angled prisms together, and the four right-angled faces of the two right-angled prisms are the first, second, third, and fourth working faces of the first polarizing beam splitter (133a), respectively; the incident beam enters through the first beam splitting face of the second polarizing beam splitter (132a); the second polarizing beam splitter (132a)... The second working surface is located on the opposite side of the first working surface; the first working surface of the third polarizing beam splitter (133a) is behind the second beam splitting surface of the second polarizing beam splitter (132a); the second collimating objective lens group (131) is located behind the third working surface of the second polarizing beam splitter (132a); the first polarizer (134a) is located behind the fourth working surface of the second polarizing beam splitter (132a); the second working surface of the third polarizing beam splitter (133a) is located on the opposite side of the first working surface, and the optical axis is... The second quarter-wave plate (133a) with an optical axis of 22.5° is located behind the second working surface of the third polarizing beam splitter (132b), the third quarter-wave plate (133b) with an optical axis of 45° is located behind the third working surface of the third polarizing beam splitter (132b), the reference mirror (135) is located behind the third quarter-wave plate (133b) with an optical axis of 45°, and the second polarizer (134b) is located behind the fourth working surface of the third polarizing beam splitter (132a).

10. A single-beam three-degree-of-freedom measurement device based on heterodyne interferometry and self-collimation according to claim 5, characterized in that, The circuit module (3) includes a photoelectric detection module (31) and a signal processing board (32). The photoelectric detection module (31) is connected to the signal processing board (32) via wires.

11. A single-beam three-degree-of-freedom measurement device based on heterodyne interferometry and self-collimation according to claim 10, characterized in that, The photoelectric detection module (31) includes a first converging collimator (311a), a second converging collimator (311b), a spot position sensor (312), a first photodetector (313a), and a second photodetector (313b). The spot position sensor (312) receives signals from the self-collimating module (12), is set on the third beam splitting surface of the first polarizing beam splitter (121), and is located at the focal plane of the reflected light. It is used to receive the reflected light and obtain the sway angle of the object around two coordinate axes that are orthogonal to the beam propagation direction and mutually perpendicular. The first photodetector (313a) and the second photodetector (313b) receive signals from the heterodyne interferometer module (13). The first photodetector (313a) is located on the focal plane of the first converging collimator (311a), and the second photodetector (313b) is located on the focal plane of the second converging collimator (311b). The first photodetector (313a) is located behind the first polarizer (134a), and the second photodetector (313b) is located behind the second polarizer (134b).

12. A single-beam three-degree-of-freedom measurement device based on heterodyne interferometry and self-collimation according to claim 10, characterized in that, The signal processing board (32) is connected to the spot position sensor (312), the first photodetector (313a), and the second photodetector (313b) via wires.

13. A single-beam three-degree-of-freedom measurement device based on heterodyne interferometry and self-collimation according to claim 11, characterized in that, The spot position sensor (312) includes a PSD, QPD, CMOS sensor or CCD sensor.

14. A single-beam three-degree-of-freedom measurement device based on heterodyne interferometry and self-collimation according to claim 8, characterized in that, The first collimating objective lens group (122) is divided into multiple objective lenses, including a collimating lens group (122a), a front lens group (122b), a first rear lens group (112c), and a second rear lens group (122d). The collimating lens group (122a) is located on the first working surface of the first polarizing beam splitter (121), the front lens group (122b) is located between the first working surface of the first polarizing beam splitter (121) and the collimating lens group (122a), and the first rear lens group (112d)... The second working surface is located on the first polarizing beam splitter (121); the second rear mirror group (122d) is located on the third working surface of the first polarizing beam splitter (121); wherein the collimating mirror group (122a) is used to collimate the first incident beam (41a), the front mirror group (122b) is used to expand the beam, the first rear mirror group (112c) is used to collimate the beam, and the first rear mirror group (112c) and the second rear mirror group (122d) are used to converge the beam.

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