A three-degree-of-freedom laser interferometry measurement device

Abstract

The present invention discloses a three-degree-of-freedom laser interferometry measurement device, comprising: a laser emitting module, a laser beam splitting module, an interference signal generating module, and a signal processing module, which are sequentially arranged. The interference signal generating module includes first and second interference signal generating modules arranged in parallel. The laser emitting module emits a laser beam. The laser beam splitting module splits the laser beam into two sub-beams with different frequencies. The two sub-beams enter two spatially separated optical paths of the first interference signal generating module, respectively obtaining a first measuring light and a first reference light, and forming a first interference signal. The two sub-beams simultaneously enter two spatially separated optical paths of the second interference signal generating module, respectively obtaining a second measuring light and a second reference light, and forming a second interference signal. The signal processing module processes the first and second interference signals to obtain the pitch angle, yaw angle, and longitudinal displacement of the target to be measured. The present invention can significantly reduce optical nonlinear errors and obtain high-precision three-degree-of-freedom values.

Description

Technical Field

[0001] The invention belongs to the technical field of precision measurement, and in particular relates to a three-degree-of-freedom laser interferometry measurement device. Background Art

[0002] Measurement is the foundation of all scientific research and industrial production. Precision measurement refers to measurements performed at millimeter-level or higher accuracy. The rise of nanometer-level ultra-precision machining technology has posed new challenges to the accuracy of ultra-precision testing. The demand for nanometer-level and even sub-nanometer measurement accuracy makes traditional contact measurement technology inadequate due to its poor real-time performance and the susceptibility to damage of measuring components.

[0003] Laser interferometry displacement measurement technology is a measurement technology that uses laser wavelength as a scale to sense displacement information through the frequency and phase changes of the interference spot. It is widely used in material geometric property characterization, precision sensor calibration, precision motion testing and high-end equipment integration due to its non-contact, high-precision, high dynamic and direct traceability of measurement results.

[0004] However, in actual measurement, the target cannot perform ideal single-axis motion. Its motion is often accompanied by posture changes and lateral displacement. The resulting measurement errors can significantly limit the accuracy of single-degree-of-freedom laser interferometers. To address this issue, laser interferometers have evolved from single-degree-of-freedom displacement measurement to three-degree-of-freedom displacement-angle simultaneous measurement. However, existing laser interferometers have numerous optical components, complex structures, and are difficult to assemble. Summary of the Invention

[0005] The purpose of the present invention is to provide a three-degree-of-freedom laser interferometer measuring device to solve the technical problems of the existing laser interferometer measuring devices, such as numerous optical elements, complex structure and great difficulty in adjustment and assembly.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A three-degree-of-freedom laser interferometry measuring device, comprising:

[0008] A laser emission module, a laser beam splitting module, an interference signal generating module and a signal processing module are arranged in sequence, wherein the interference signal generating module is communicatively connected to the signal processing module, and the interference signal generating module includes a first interference signal generating module and a second interference signal generating module arranged in parallel;

[0009] Wherein, the laser emitting module emits a laser beam to the laser beam splitting module;

[0010] The laser beam splitting module splits the laser beam into a first sub-beam and a second sub-beam with different frequencies and injects the sub-beams into the first interference signal generating module and the second interference signal generating module;

[0011] The first interference signal generating module includes a first photodetector, a first sub-optical path and a second sub-optical path with spatially separated optical paths, the first sub-optical path and the second sub-optical path are arranged in parallel in front of the first photodetector, the first sub-beam forms a first measuring light on the first sub-optical path, the second sub-beam forms a first reference light on the second sub-optical path, and the first reference light and the first measuring light interfere on the first photodetector to form a first interference signal;

[0012] The second interference signal generating module includes a second photodetector, a third sub-optical path and a fourth sub-optical path with spatially separated optical paths, the third sub-optical path and the fourth sub-optical path are arranged in parallel in front of the second photodetector, the first sub-beam forms a second measuring light on the third sub-optical path, the second sub-beam forms a second reference light on the fourth sub-optical path, and the second reference light and the second measuring light interfere on the second photodetector to form a second interference signal;

[0013] The signal processing module converts the first interference signal into a noise floor during the interferometric measurement process, and uses the noise floor to perform noise compensation on a voltage signal converted from the second interference signal, thereby ultimately obtaining the pitch angle, yaw angle, and longitudinal displacement of the target to be measured.

[0014] Optionally, the laser beam splitting module includes:

[0015] a first beam splitter prism, a first acousto-optic frequency shifter, a second acousto-optic frequency shifter, a first reflector, a first fiber coupler, a second fiber coupler, a first collimating lens, and a second collimating lens;

[0016] The first acousto-optic frequency shifter and the first reflector are correspondingly arranged behind the first beam splitter prism, the first fiber coupler and the first collimating lens are sequentially arranged behind the first acousto-optic frequency shifter, and the second acousto-optic frequency shifter, the second fiber coupler, and the second collimating lens are sequentially arranged behind the first reflector.

[0017] The first beam splitter splits the laser beam into mutually perpendicular reflected light and transmitted light, the first acousto-optic frequency shifter shifts the frequency of the transmitted light, the first fiber coupler couples the frequency-shifted transmitted light, and the first collimating lens converts the coupled transmitted light into parallel light as a first sub-beam; the first reflector reflects the reflected light to the second acousto-optic frequency shifter, the second acousto-optic frequency shifter shifts the frequency of the reflected light, the second fiber coupler couples the frequency-shifted reflected light, and the second collimating lens converts the coupled reflected light into parallel light as a second sub-beam.

[0018] Optionally, the first sub-optical path includes:

[0019] The second beam splitter prism and the second reflector are correspondingly provided, and the first sub-beam is reflected by the second beam splitter prism and the second reflector in sequence and then reaches the first photodetector to form the first measuring light.

[0020] Optionally, the first reflector is a 45° reflector.

[0021] Optionally, the second sub-optical path includes:

[0022] The third beam splitter prism and the fourth beam splitter prism are vertically arranged, and the second sub-beam is reflected by the third beam splitter prism and the fourth beam splitter prism in sequence and then reaches the first photodetector to form the first reference light.

[0023] Optionally, the third sub-light path includes:

[0024] The target reflector and the second beam splitter prism are fixed on the target to be measured. The first sub-beam is reflected by the target reflector and the second beam splitter prism in sequence and then reaches the second photoelectric detector to form the second measuring light.

[0025] Optionally, the fourth sub-light path includes:

[0026] A fifth beam splitter prism is provided, wherein the second sub-beam is reflected by the fifth beam splitter prism and reaches the second photodetector to form a second reference light.

[0027] Optionally, the signal processing module includes:

[0028] A first photoelectric conversion unit, a second photoelectric conversion unit, an adjustable gain control unit, an anti-aliasing filter unit, an AD sampling unit, a digital phase meter, and a three-degree-of-freedom solving unit are sequentially arranged after the adjustable gain control unit;

[0029] Wherein, the first photoelectric conversion unit is connected to the first photodetector and the adjustable gain control unit, the second photoelectric conversion unit is connected to the second photodetector and the adjustable gain control unit, and the adjustable gain control unit is connected to the first photoelectric conversion unit, the second photoelectric conversion unit, and the anti-aliasing filter unit;

[0030] The first photoelectric conversion unit converts the first interference signal into a noise floor in the interference measurement process, the second photoelectric conversion unit converts the second interference signal into a voltage signal, the adjustable gain control unit performs noise compensation on the voltage signal according to the noise floor and outputs a signal with a fixed intensity, the anti-aliasing filter unit is used to filter out interference signals, the AD sampling unit is used to convert the collected analog signal into a digital signal, the digital phase meter is used to obtain phase information based on the digital signal, and the three-degree-of-freedom solver obtains the pitch angle, the yaw angle and the longitudinal displacement of the target to be measured based on the phase information.

[0031] Optionally, the second photodetector is a four-quadrant photodetector.

[0032] Optionally, the laser emission module is a frequency-stabilized laser.

[0033] The present invention provides a three-degree-of-freedom laser interferometer measurement device, comprising: a laser emitting module, a laser beam splitting module, an interference signal generating module and a signal processing module arranged in sequence, wherein the interference signal generating module is communicatively connected to the signal processing module, and the interference signal generating module comprises a first interference signal generating module and a second interference signal generating module arranged in parallel; wherein the laser emitting module emits a laser beam to the laser beam splitting module; the laser beam splitting module splits the laser beam into a first sub-beam and a second sub-beam with different frequencies and injects the first and second sub-beams into the first and second interference signal generating modules; the first interference signal generating module comprises a first photodetector, a first sub-optical path and a second sub-optical path separated in optical path space, the first sub-optical path and the second sub-optical path are arranged in parallel in front of the first photodetector, and the first sub-optical beam forms a first measuring light on the first sub-optical path. The second sub-beam forms a first reference light on the second sub-optical path, and the first reference light and the first measuring light interfere on the first photodetector to form a first interference signal; the second interference signal generating module includes a second photodetector, a third sub-optical path and a fourth sub-optical path separated in optical path space, the third sub-optical path and the fourth sub-optical path are arranged in parallel in front of the second photodetector, the first sub-beam forms a second measuring light on the third sub-optical path, the second sub-beam forms a second reference light on the fourth sub-optical path, and the second reference light and the second measuring light interfere on the second photodetector to form a second interference signal; the signal processing module converts the first interference signal into a noise floor in the interferometric measurement process, and uses the noise floor to perform noise compensation on the voltage signal converted from the second interference signal, and finally obtains the pitch angle, yaw angle and longitudinal displacement of the target to be measured.

[0034] In view of this, the beneficial effects brought by the present invention are:

[0035] The present invention utilizes a laser beam splitting module to split the laser beam emitted by the laser emission module into two sub-beams with different frequencies, utilizes a dual-frequency laser to perform interference measurement, and has stronger anti-interference ability; the interference signal generation module includes a first and a second interference signal generation module arranged in parallel, wherein the first sub-optical path forming the first measurement light and the second sub-optical path forming the first reference light in the first interference signal generation module are spatially separated from each other, and the first measurement light and the first reference light interfere to obtain a first interference signal; the third sub-optical path forming the second measurement light and the fourth sub-optical path forming the second reference light in the second interference signal generation module are spatially separated from each other, and the second measurement light and the second reference light interfere to obtain a second interference signal, significantly reducing optical nonlinear error by means of optical path spatial separation; the signal processing module uses the noise floor obtained by converting the first interference signal to perform noise compensation on the second interference signal, thereby obtaining high-precision pitch angle, yaw angle and longitudinal displacement of the target to be measured. The present invention has fewer optical components, a simple and compact structure, and is easy to adjust and assemble, and also has the advantages of effectively suppressing nonlinear error, self-compensation of interference measurement noise, and simultaneous measurement of multiple degrees of freedom. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a structural schematic diagram of the present invention;

[0037] Figure 2 is a three-dimensional schematic diagram of an embodiment of the present invention;

[0038] Among them, there are a frequency-stabilized laser 1, a first beam splitter prism 2, a first acousto-optic frequency shifter 3, a first fiber coupler 4, a first photoelectric conversion unit 5, a first photodetector 6, a first collimating lens 7, a fourth beam splitter prism 8, a second reflector 9, a second beam splitter prism 10, a movable target reflector 11, a fifth beam splitter prism 12, a second photodetector 13, a third beam splitter prism 14, a second photoelectric conversion unit 15, a second collimating lens 16, an adjustable gain control unit 17, an anti-aliasing filter unit 18, a second fiber coupler 19, an AD sampling unit 20, a digital phase meter 21, a three-degree-of-freedom solver 22, a first reflector 23, and a second acousto-optic frequency shifter 24. DETAILED DESCRIPTION

[0039] The embodiment of the present invention provides a three-degree-of-freedom laser interferometer measurement device to solve the technical problems of the existing laser interferometer measurement device, such as numerous optical elements, complex structure, and difficult adjustment and assembly.

[0040] To facilitate understanding of the present invention, the present invention will be described more fully below with reference to the accompanying drawings. Preferred embodiments of the present invention are shown in the drawings. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive disclosure of the present invention.

[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used in this specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0042] Laser interferometers can be divided into single-frequency laser interferometers and dual-frequency laser interferometers. The interference signal of a single-frequency laser interferometer is easily affected by changes in optical power and environmental fluctuations, and there is a DC drift problem. The dual-frequency laser interferometer uses a dual-frequency light source to make the output signal an AC signal, which directly eliminates the error caused by DC drift in the single-frequency laser interferometer and improves the anti-interference capability. However, the use of a dual-frequency light source will introduce optical nonlinear errors. The nonlinear errors mainly come from frequency aliasing caused by the ellipsometry and non-orthogonality of the laser light source, polarization aliasing caused by polarization leakage of the beam splitter prism, and optical ghost reflections. Spatial beam separation is one of the methods to suppress the nonlinear errors of dual-frequency laser interferometers. By separating the spatial paths of light of different frequencies, frequency aliasing and polarization aliasing can be eliminated from the source, thereby greatly reducing optical nonlinear errors.

[0043] In actual measurement, the target to be measured cannot perform ideal single-axis motion. Its motion is often accompanied by posture changes and lateral displacement. The resulting longitudinal displacement measurement error greatly limits the measurement accuracy of single-degree-of-freedom laser interferometers. To address this problem and simultaneously meet the requirements for high-precision measurement of various micro-components, complex surfaces, microelectronic devices, and precision optical elements, laser interferometry devices have evolved from single-degree-of-freedom displacement measurement to three-degree-of-freedom simultaneous displacement-angle measurement. By measuring the two-dimensional angular information of the target to be measured, the displacement measurement results are corrected, further improving measurement accuracy.

[0044] The purpose of the present invention is to address the shortcomings of existing multi-degree-of-freedom high-precision heterodyne laser interferometers and propose a high-precision three-degree-of-freedom laser interferometer measurement device with spatially separated optical paths and noise compensation, so as to achieve the purpose of comprehensively improving the measurement accuracy of the heterodyne laser interferometer.

[0045] See also Figure 1 The present invention provides an embodiment of a three-degree-of-freedom laser interferometry device, comprising:

[0046] A laser emission module, a laser beam splitting module, an interference signal generating module and a signal processing module are arranged in sequence, wherein the interference signal generating module is communicatively connected to the signal processing module, and the interference signal generating module includes a first interference signal generating module and a second interference signal generating module arranged in parallel;

[0047] Wherein, the laser emitting module emits a laser beam to the laser beam splitting module;

[0048] The laser beam splitting module splits the laser beam into a first sub-beam and a second sub-beam with different frequencies and injects the sub-beams into the first interference signal generating module and the second interference signal generating module;

[0049] The first interference signal generating module includes a first photodetector, a first sub-optical path and a second sub-optical path with spatially separated optical paths, the first sub-optical path and the second sub-optical path are arranged in parallel in front of the first photodetector, the first sub-beam forms a first measuring light on the first sub-optical path, the second sub-beam forms a first reference light on the second sub-optical path, and the first reference light and the first measuring light interfere on the first photodetector to form a first interference signal;

[0050] The second interference signal generating module includes a second photodetector, a third sub-optical path and a fourth sub-optical path with spatially separated optical paths, the third sub-optical path and the fourth sub-optical path are arranged in parallel in front of the second photodetector, the first sub-beam forms a second measuring light on the third sub-optical path, the second sub-beam forms a second reference light on the fourth sub-optical path, and the second reference light and the second measuring light interfere on the second photodetector to form a second interference signal;

[0051] The signal processing module converts the first interference signal into a noise floor during the interferometric measurement process, and uses the noise floor to perform noise compensation on a voltage signal converted from the second interference signal, thereby ultimately obtaining the pitch angle, yaw angle, and longitudinal displacement of the target to be measured.

[0052] The three-degree-of-freedom laser interferometry device provided in this embodiment is a high-precision three-degree-of-freedom laser interferometry device with spatially separated optical paths and noise compensation. The device comprises: a laser emission module, a laser beam splitting module, an interference signal generation module, and a signal processing module, which are arranged in sequence; wherein the laser emission module can be a frequency-stabilized laser, and the laser beam splitting module can include: a first beam splitting prism 2, a first acousto-optic frequency shifter 3, a first reflector 23, a second acousto-optic frequency shifter 24, a first fiber coupler 4, a second fiber coupler 19, a first collimating lens 7, and a second collimating lens 16;

[0053] The first acousto-optic frequency shifter 3 and the first reflector 23 are correspondingly arranged behind the first beam splitter prism 2, the first fiber coupler 4 and the first collimating lens 7 are sequentially arranged behind the first acousto-optic frequency shifter 3, and the second acousto-optic frequency shifter 24, the second fiber coupler 19, and the second collimating lens 16 are sequentially arranged behind the first reflector 23;

[0054] The first beam splitter prism 2 divides the laser beam into mutually perpendicular reflected light and transmitted light, the first acousto-optic frequency shifter 3 shifts the frequency of the transmitted light, the first fiber coupler 4 couples the frequency-shifted transmitted light, and the first collimating lens 7 converts the coupled transmitted light into parallel light as the first sub-beam; the first reflector 23 reflects the reflected light to the second acousto-optic frequency shifter 24, the second acousto-optic frequency shifter 24 shifts the frequency of the reflected light, the second fiber coupler 19 couples the frequency-shifted reflected light, and the second collimating lens 16 converts the coupled reflected light into parallel light as the second sub-beam.

[0055] Specifically, a frequency-stabilized laser 1 emits a laser beam with a frequency of f0. This laser beam passes through a first beam splitter prism 2 and is split into two mutually perpendicular beams of reflected light and transmitted light. The laser light (transmitted light) transmitted through the first beam splitter prism 2 is frequency-shifted by a first acousto-optic frequency shifter 3 to a frequency of f0 + f1, where f1 is the frequency shift amount of the first acousto-optic frequency shifter 3. The frequency-shifted laser light is coupled into a first fiber coupler 4 and then returns to free space as signal light. The signal light is converted into a parallel beam by a first collimating lens 7 and serves as the first sub-beam. The laser light (i.e., reflected light) reflected by the first beam splitter prism 2 is reflected by a first reflector 23 and then frequency-shifted by a second acousto-optic frequency shifter 24 to a frequency of f0 + f2, where f2 is the frequency shift amount of the second acousto-optic frequency shifter 24. The frequency-shifted laser light is coupled into a second fiber coupler 19 and then returns to free space as local oscillator light. The local oscillator light is converted into a parallel beam by a second collimating lens 16 and serves as the second sub-beam.

[0056] It should be noted that the frequency-stabilized laser emits a single-frequency laser. The dual-frequency laser in this device is achieved by splitting the single-frequency light emitted by the frequency-stabilized laser and passing it through the first and second acousto-optic frequency shifters respectively (the frequency shift amounts of the first acousto-optic frequency shifter and the second acousto-optic frequency shifter are different, that is, f1≠f2).

[0057] It should be noted that free space is relative to the space inside the optical fiber. The laser enters the optical fiber through the fiber coupler and then returns to the free space. The local oscillator light eventually forms the reference light (the first reference light or the second reference light), and the signal light eventually forms the measurement light (the first measurement light or the second measurement light). The first reference light and the first measurement light form a first beat signal (i.e., a first interference signal). The first beat signal is photoelectrically converted to obtain a noise floor. The second reference light and the second measurement light form a second beat signal (i.e., a second interference signal).

[0058] In this embodiment, the first interference signal generating module includes a first photodetector 6, a first sub-optical path and a second sub-optical path with spatially separated optical paths. The first sub-optical path and the second sub-optical path are arranged in parallel in front of the first photodetector 6. The first sub-light beam propagates on the first sub-optical path and forms a first measuring light. The second sub-light beam propagates on the second sub-optical path and forms a first reference light. The first reference light and the first measuring light interfere on the first photodetector 6 to form a first interference signal with a frequency of |f2-f1|.

[0059] In one embodiment of the present invention, the first sub-optical path may include: a corresponding second beam splitter prism 10 and a second reflector 9. The first sub-beam is reflected by the second beam splitter prism 10 and the second reflector 9 in sequence and then reaches the first photodetector 6 to form the first measuring light.

[0060] The second sub-light path may include: a third beam splitter prism 14 and a fourth beam splitter prism 8 arranged vertically. The second sub-beam is reflected by the third beam splitter prism 14 and the fourth beam splitter prism 8 in sequence and then reaches the first photodetector 6 to form the first reference light.

[0061] It should be noted that, in this embodiment, the reflective surfaces of the first reflector and the second reflector are both placed at 45° to the incident light and the reflected light.

[0062] In this embodiment, the second interference signal generating module includes a second photodetector 13, a third sub-optical path and a fourth sub-optical path with spatially separated optical paths. The third sub-optical path and the fourth sub-optical path are arranged in parallel in front of the second photodetector 13. The first sub-beam propagates on the third sub-optical path and forms a second measuring light. The second sub-beam propagates on the fourth sub-optical path and forms a second reference light. The second reference light and the second measuring light interfere on the second photodetector 13 to form a second interference signal with a frequency of |f2-f1|.

[0063] In this embodiment, the third sub-optical path includes: a target reflector 11 fixed on the target to be measured and a second beam splitter prism 10. The first sub-beam is reflected by the target reflector 11 and the second beam splitter prism 10 in sequence and then reaches the second photodetector 13 to form the second measuring light.

[0064] The fourth sub-optical path may include: a fifth beam splitter prism 12 , and the second sub-beam is reflected by the fifth beam splitter prism 12 and reaches the second photodetector 13 to form a second reference light.

[0065] In one embodiment of the present invention, the signal processing module may include:

[0066] A first photoelectric conversion unit 5, a second photoelectric conversion unit 15, an adjustable gain control unit 17, an anti-aliasing filter unit 18, an AD sampling unit 20, a digital phase meter 21, and a three-degree-of-freedom solving unit 22 are sequentially arranged after the adjustable gain control unit;

[0067] The first photoelectric conversion unit 5 is connected to the first photodetector 6 and the adjustable gain control unit 17, the second photoelectric conversion unit 15 is connected to the second photodetector 13 and the adjustable gain control unit 17, and the adjustable gain control unit 17 is connected to the first photoelectric conversion unit 5, the second photoelectric conversion unit 15, and the anti-aliasing filter unit 18;

[0068] The first photoelectric conversion unit 5 converts the first interference signal into the noise floor in the interference measurement process, the second photoelectric conversion unit 15 converts the second interference signal into a voltage signal, the adjustable gain control unit 17 performs noise compensation on the voltage signal according to the noise floor and outputs a signal with a fixed intensity, the anti-aliasing filter unit 18 is used to filter out the interference signal, the AD sampling unit 20 is used to convert the collected analog signal into a digital signal, the digital phase meter 21 is used to obtain phase information based on the digital signal, and the three-degree-of-freedom solver 22 obtains the pitch angle, yaw angle and longitudinal displacement of the target to be measured based on the phase information.

[0069] In this embodiment, the first photodetector 6 can be a four-quadrant photodetector or a single-quadrant photodetector, and the second photodetector 13 can be a four-quadrant photodetector. Since the second photodetector 13 uses differential wavefront sensing technology to measure the two-dimensional angles of the target reflector, the yaw angle and the pitch angle, a four-quadrant photodetector is required, as a single-quadrant photodetector cannot measure angles.

[0070] It should be noted that the adjustable gain control unit 17 is a variable gain amplifier, whose function is to convert interference signals of different intensities into signal outputs of fixed intensity; the function of the three-degree-of-freedom solver 22 is to convert the phase information output by the digital phase meter into two-dimensional angle information and longitudinal displacement information.

[0071] The three-degree-of-freedom laser interferometry measurement device provided by this embodiment uses a laser beam splitting module to split the laser beam emitted by the laser emission module into two sub-beams with different frequencies, and uses a dual-frequency laser to perform interference measurement, which has stronger anti-interference ability; the interference signal generation module includes a first and a second interference signal generation module arranged in parallel, wherein the first sub-optical path forming the first measurement light and the second sub-optical path forming the first reference light in the first interference signal generation module are spatially separated from each other, and the first measurement light and the first reference light interfere to obtain a first interference signal; the third sub-optical path forming the second measurement light and the fourth sub-optical path forming the second reference light in the second interference signal generation module are spatially separated from each other, and the second measurement light and the second reference light interfere to obtain a second interference signal, which significantly reduces the optical nonlinear error by separating the optical paths; the signal processing module uses the noise floor obtained by converting the first interference signal to compensate the second interference signal for noise, and obtains the high-precision pitch angle, yaw angle and longitudinal displacement of the target to be measured. The present invention has fewer optical components, a simple and compact structure, and is easy to adjust and assemble. It also has the advantages of effectively suppressing nonlinear errors, self-compensating interference measurement noise, and simultaneous measurement of multiple degrees of freedom.

[0072] See also Figure 2 The present invention provides another embodiment of a three-degree-of-freedom laser interferometry measuring device, comprising:

[0073] A frequency-stabilized laser 1, a first beam splitter prism 2, a first reflector 23, a first acousto-optic frequency shifter 3, a first fiber coupler 4, a first collimating lens 7, a target reflector 11, a second beam splitter prism 10, a third beam splitter prism 14, a first photodetector 6, a second acousto-optic frequency shifter 24, a second fiber coupler 19, a second collimating lens 16, a fourth beam splitter prism 8, a second reflector 9, a first photoelectric conversion unit 5, a fifth beam splitter prism 12, a second photodetector 13, a second photoelectric conversion unit 15, an adjustable gain control unit 17, an anti-aliasing filter unit 18, an AD sampling unit 20, a digital phase meter 21, and a three-degree-of-freedom solver 22;

[0074] Among them, the frequency-stabilized laser 1, the first beam splitter prism 2, the first reflector 23, the first acousto-optic frequency shifter 3, the first fiber coupler 4, the first collimating lens 7, the second beam splitter prism 10, the third beam splitter prism 14, the first photodetector 6, the second acousto-optic frequency shifter 24, the second fiber coupler 19, the second collimating lens 16, the fourth beam splitter prism 8, and the second reflector 9 constitute a reference interferometer; the frequency-stabilized laser 1, the first beam splitter prism 2, the first reflector 23, the first acousto-optic frequency shifter 3, the first fiber coupler 4, the first collimating lens 7, the target reflector 11, the second beam splitter prism 10, the second photodetector 13, the second acousto-optic frequency shifter 24, the second fiber coupler 19, the second collimating lens 16, and the fourth beam splitter prism 8 constitute a measuring interferometer.

[0075] In this embodiment, the frequency-stabilized laser 1 emits a laser beam with a frequency of f0, which is divided into two beams by the first beam splitter prism 2. The laser beam reflected by the first beam splitter prism 2 is reflected by the first reflector 23 and then shifted to a frequency of f0+f2 by the second acousto-optic frequency shifter 24. The laser beam is coupled into the second fiber coupler 19 and then returns to the free space as the local oscillation light. The local oscillation light is converted into a parallel beam by the second collimating lens 16 and then reflected by the second beam splitter prism 14 and the fourth beam splitter prism 8 to reach the first photodetector 6 as the reference light of the reference interferometer. The laser beam transmitted by the first beam splitter prism 2 is shifted to a frequency of f0+f2 by the first acousto-optic frequency shifter 3. 0+f1, the laser is coupled into the first fiber coupler 4 and then returns to the free space as the signal light. The signal light is converted into a parallel beam by the first collimating lens, and then reflected by the second beam splitter prism 10 and the second reflector 9 to reach the first photodetector 6 as the measurement light of the reference interferometer. The reference light and the measurement light form a beat signal with a frequency of |f2-f1| on the first photodetector 6, and the noise floor in the interference measurement process is obtained by the first photoelectric conversion unit 5. The reference light and the measurement light in the reference interferometer pass through different optical elements during the interference measurement process, and the reference light path and the measurement light path are spatially separated from each other.

[0076] At the same time, the local oscillator light is converted into a parallel beam after passing through the second collimating lens 16, and then reflected by the third beam splitter prism 14 to reach the second photodetector 13, or is transmitted through the third beam splitter prism 14 and reflected by the fifth beam splitter prism 12 in sequence to reach the second photodetector 13, serving as the reference light of the measuring interferometer; the signal light is converted into a parallel beam after passing through the first collimating lens 7, and then reflected by the movable target reflector 11 and the second beam splitter prism 10 to reach the second photodetector 13, serving as the measuring light of the measuring interferometer; the reference light and the measuring light form a beat signal with a frequency of |f2-f1| on the second photodetector 13, and based on the differential wavefront sensing technology, after being processed by the second photoelectric conversion unit 15, the adjustable gain control unit 17, the anti-aliasing filter unit 18, the AD sampling unit 20, the digital phase meter 21 and the three-degree-of-freedom solver 22, the measurement quantities of the two-dimensional deflection angle and longitudinal displacement of the target reflector 11 are obtained. The reference light and the measuring light in the measuring interferometer each pass through different optical elements during the interferometric measurement process, and the reference light path and the measuring light path are spatially separated from each other.

[0077] During the interference signal processing process, the signal processing module uses the second photoelectric conversion unit 15 to convert the interference signal obtained by the measuring interferometer into a voltage signal. This voltage signal is then noise-compensated using the interferometer noise floor measured by the reference interferometer, ultimately obtaining a high-precision three-degree-of-freedom measurement result for the target reflector. Because the target reflector is fixed to the object to be measured, the measured three-degree-of-freedom information of the target reflector is equivalent to the three-degree-of-freedom information of the object to be measured.

[0078] It should be noted that the interference signal, i.e., the signal formed on the photodetector when the measuring light interferes with the reference light, is equivalent to the beat signal. The measuring light in the reference interferometer interferes with the reference light to form an interference signal on the first photodetector, and the measuring light in the measuring interferometer interferes with the reference light to form an interference signal on the second photodetector.

[0079] It should be noted that the first, second, third, fourth and fifth beam splitters in the present invention can be ordinary beam splitters or depolarizing beam splitters. The present invention has no special requirements on the size and splitting ratio of the beam splitters, but polarizing beam splitters are not applicable to the present invention.

[0080] In the present invention, the reflecting surfaces of the first and second reflectors and the first, second, third, fourth and fifth beam splitter prisms are all at 45° to the incident light except the light reflected by the target reflector; the present invention has no strict requirements on the positions of the reflectors and beam splitter prisms, as long as the reference light and the measurement light of the reference interferometer and the reference light of the measurement interferometer are all incident on the centers of the first and second photodetectors.

[0081] In this embodiment, the first photodetector 6 may be a four-quadrant photodetector or a single-quadrant photodetector, and the second photodetector 13 is a four-quadrant photodetector.

[0082] In the interference signal processing, the interferometer noise floor measured by the reference interferometer is used to compensate the interference signal of the measurement interferometer, and finally a high-precision three-degree-of-freedom measurement result of the target reflector is obtained.

[0083] The three-degree-of-freedom laser interferometry measurement device provided in this embodiment adopts a dual-frequency laser interferometry measurement method with stronger anti-interference capability, and eliminates optical nonlinear errors from the root by spatially separating the optical paths; noise compensation is performed on the measurement results of the measuring interferometer by using the interferometer noise floor measured by the reference interferometer; high-precision two-dimensional angular information of the target reflector is measured based on differential wavefront sensing technology; the present invention involves fewer optical elements, has a compact structure, and is easy to adjust and install.

[0084] Compared with the existing laser interferometry measurement system, the device of the present invention has the advantages of effectively suppressing nonlinear errors, self-compensation of interferometry noise, simple and compact structure, and simultaneous measurement of multiple degrees of freedom.

[0085] The present invention has the following characteristics and advantages:

[0086] (1) In the present invention, the reference light and the measurement light of the reference interferometer and the measurement interferometer are spatially separated, which fundamentally eliminates the frequency aliasing caused by the elliptical polarization and non-orthogonality of the laser light source and the polarization aliasing caused by the polarization leakage of the beam splitter prism, thereby significantly reducing the optical nonlinear error.

[0087] (2) In the present invention, the reference interferometer is used to measure the noise floor of the three-degree-of-freedom laser interferometer measurement device itself, and the three-degree-of-freedom motion information of the target reflector measured by the reference interferometer is noise compensated to further improve the measurement accuracy.

[0088] (3) In the present invention, the signal receiving end of the measuring interferometer adopts a four-quadrant photoelectric detector, which can simultaneously measure the longitudinal displacement information and two-dimensional angular deflection information of the target reflector.

[0089] Those skilled in the art will clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0090] In the embodiments provided in this application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are merely schematic. For example, the division of the units is only a logical function division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or units, which can be electrical, mechanical or other forms.

[0091] The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of these units may be selected to achieve the purpose of this embodiment according to actual needs.

[0092] In addition, the functional units in the various embodiments of the present invention may be integrated into a single processing unit, each unit may exist physically separately, or two or more units may be integrated into a single unit. The aforementioned integrated units may be implemented in the form of hardware or software functional units.

[0093] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for enabling a computer device (which can be a personal computer, server, or network device, etc.) to execute all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: various media that can store program codes, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk.

[0094] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A three-degree-of-freedom laser interferometer measuring device, characterized in that: include: A laser emission module, a laser beam splitting module, an interference signal generating module and a signal processing module are arranged in sequence, wherein the interference signal generating module is communicatively connected to the signal processing module, and the interference signal generating module includes a first interference signal generating module and a second interference signal generating module arranged in parallel; Wherein, the laser emitting module emits a laser beam to the laser beam splitting module; The laser beam splitting module splits the laser beam into a first sub-beam and a second sub-beam with different frequencies and injects the sub-beams into the first interference signal generating module and the second interference signal generating module; The first interference signal generating module includes a first photodetector, a first sub-optical path and a second sub-optical path with spatially separated optical paths, the first sub-optical path and the second sub-optical path are arranged in parallel in front of the first photodetector, the first sub-beam forms a first measuring light on the first sub-optical path, the second sub-beam forms a first reference light on the second sub-optical path, and the first reference light and the first measuring light interfere on the first photodetector to form a first interference signal; The second interference signal generating module includes a second photodetector, a third sub-optical path and a fourth sub-optical path with spatially separated optical paths, the third sub-optical path and the fourth sub-optical path are arranged in parallel in front of the second photodetector, the first sub-beam forms a second measuring light on the third sub-optical path, the second sub-beam forms a second reference light on the fourth sub-optical path, and the second reference light and the second measuring light interfere on the second photodetector to form a second interference signal; The signal processing module converts the first interference signal into a noise floor during the interferometric measurement process, and uses the noise floor to perform noise compensation on a voltage signal converted from the second interference signal, thereby ultimately obtaining a pitch angle, a yaw angle, and a longitudinal displacement of the target to be measured; The laser beam splitting module includes: a first beam splitting prism, a first acousto-optic frequency shifter, a second acousto-optic frequency shifter, a first reflector, a first fiber coupler, a second fiber coupler, a first collimating lens and a second collimating lens; The first acousto-optic frequency shifter and the first reflector are correspondingly arranged behind the first beam splitter prism, the first fiber coupler and the first collimating lens are sequentially arranged behind the first acousto-optic frequency shifter, and the second acousto-optic frequency shifter, the second fiber coupler, and the second collimating lens are sequentially arranged behind the first reflector. The first beam splitter splits the laser beam into a reflected light and a transmitted light perpendicular to each other; the first acousto-optic frequency shifter shifts the frequency of the transmitted light; the first fiber coupler couples the frequency-shifted transmitted light; the first collimating lens converts the coupled transmitted light into parallel light as a first sub-beam; the first reflector reflects the reflected light to the second acousto-optic frequency shifter; the second acousto-optic frequency shifter shifts the frequency of the reflected light; the second fiber coupler couples the frequency-shifted reflected light; the second collimating lens converts the coupled reflected light into parallel light as a second sub-beam; The first reflector is a 45° reflector.

2. The three-degree-of-freedom laser interferometer measurement device according to claim 1, characterized in that: The first sub-optical path includes: The second beam splitter prism and the second reflector are correspondingly provided, and the first sub-beam is reflected by the second beam splitter prism and the second reflector in sequence and then reaches the first photodetector to form the first measuring light.

3. The three-degree-of-freedom laser interferometer measurement device according to claim 1, characterized in that: The second sub-optical path includes: The third beam splitter prism and the fourth beam splitter prism are vertically arranged, and the second sub-beam is reflected by the third beam splitter prism and the fourth beam splitter prism in sequence and then reaches the first photodetector to form the first reference light.

4. The three-degree-of-freedom laser interferometer measurement device according to claim 1, characterized in that: The third sub-light path includes: The target reflector and the second beam splitter prism are fixed on the target to be measured. The first sub-beam is reflected by the target reflector and the second beam splitter prism in sequence and then reaches the second photoelectric detector to form the second measuring light.

5. The three-degree-of-freedom laser interferometer measurement device according to claim 1, characterized in that: The fourth sub-light path includes: A fifth beam splitter prism is provided, wherein the second sub-beam is reflected by the fifth beam splitter prism and reaches the second photodetector to form a second reference light.

6. The three-degree-of-freedom laser interferometer measurement device according to claim 1, characterized in that: The signal processing module includes: A first photoelectric conversion unit, a second photoelectric conversion unit, an adjustable gain control unit, an anti-aliasing filter unit, an AD sampling unit, a digital phase meter, and a three-degree-of-freedom solving unit are sequentially arranged after the adjustable gain control unit; Wherein, the first photoelectric conversion unit is connected to the first photodetector and the adjustable gain control unit, the second photoelectric conversion unit is connected to the second photodetector and the adjustable gain control unit, and the adjustable gain control unit is connected to the first photoelectric conversion unit, the second photoelectric conversion unit, and the anti-aliasing filter unit; The first photoelectric conversion unit converts the first interference signal into a noise floor in the interference measurement process, the second photoelectric conversion unit converts the second interference signal into a voltage signal, the adjustable gain control unit performs noise compensation on the voltage signal according to the noise floor and outputs a signal with a fixed intensity, the anti-aliasing filter unit is used to filter out interference signals, the AD sampling unit is used to convert the collected analog signal into a digital signal, the digital phase meter is used to obtain phase information based on the digital signal, and the three-degree-of-freedom solver obtains the pitch angle, the yaw angle and the longitudinal displacement of the target to be measured based on the phase information.

7. The three-degree-of-freedom laser interferometer measurement device according to claim 1, characterized in that: The second photodetector is a four-quadrant photodetector.

8. The three-degree-of-freedom laser interferometer measuring device according to any one of claims 1 to 7, characterized in that: The laser emission module is a frequency-stabilized laser.

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