A multi-order diffraction grating precision displacement sensor and a displacement measurement method

Abstract

The application discloses a multi-order diffraction grating precision displacement sensor and a displacement measurement method, and relates to the field of displacement sensors.The multi-order diffraction grating precision displacement sensor comprises a laser, a half-wave plate, a first non-polarized light splitting prism, a ±2-order diffraction interference grating precision displacement sensor module and a ±3-order diffraction interference grating precision displacement sensor module.The final displacement measurement result is obtained by weighting the noise levels of the ±2-order diffraction interference grating precision displacement sensor module and the ±3-order diffraction interference grating precision displacement sensor module and then performing calculation.The application provides the multi-order diffraction grating precision displacement sensor, uses the polarization characteristics of light to improve the application rate of effective light, reduces the interference of environmental stray light on the measurement signal, and improves the accuracy and stability of the overall system.

Description

Technical Field

[0001] This application relates to the field of displacement sensors, and in particular to a multi-order diffraction grating precision displacement sensor and displacement measurement method. Background Technology

[0002] Grating precision displacement measurement technology is a high-precision displacement measurement method based on the principles of optical diffraction and interference. It is widely used in precision manufacturing, semiconductor equipment, CNC machine tools, micro-nano technology, and scientific research instruments. Its core principle is to convert the displacement into a periodic optical signal change through the relative motion of the grating and the diffracted light, and then achieve nanometer-level or even sub-nanometer-level resolution through electronic subdivision technology.

[0003] Although grating precision displacement measurement systems based on the principle of optical diffraction interference have been widely used, their optical structures are generally designed with a preference for lower-order diffraction light (such as ±1st-order diffraction light). Theoretically, higher-order diffraction light can result in lower resolution for grating precision displacement measurement systems. Therefore, using higher-order and multi-order diffraction light to improve the resolution of grating precision displacement measurement systems is one of the important directions in designing high-precision grating displacement sensors. Summary of the Invention

[0004] The purpose of this application is to provide a multi-order diffraction grating precision displacement sensor and displacement measurement method, which can improve the resolution of the grating precision displacement measurement system and thus improve the accuracy of displacement measurement.

[0005] To achieve the above objectives, this application provides the following solution:

[0006] In a first aspect, this application provides a multi-order diffraction grating precision displacement sensor, comprising: a laser, a half-wave plate, a first non-polarizing beam splitter, a ±2nd order diffraction interference grating precision displacement sensor module, and a ±3rd order diffraction interference grating precision displacement sensor module.

[0007] The ±2nd order diffraction interference grating precision displacement sensor module includes: a second unpolarized beam splitter, a first polarized beam splitter, a first quarter-wave plate, a second quarter-wave plate, a third quarter-wave plate, a first mirror, a second mirror, a grating, a first polarizer, a second polarizer, a first photodetector, and a second photodetector.

[0008] The ±3rd order diffraction interference grating precision displacement sensor module includes: a third unpolarized beam splitter, a second polarized beam splitter, a fourth quarter-wave plate, a fifth quarter-wave plate, a sixth quarter-wave plate, a third mirror, a fourth mirror, a grating, a third polarizer, a fourth polarizer, a third photodetector, and a fourth photodetector.

[0009] Secondly, this application provides a displacement measurement method, including:

[0010] The ±2nd order diffraction interference grating precision displacement sensor module in the above-mentioned multi-order diffraction grating precision displacement sensor obtains the first interference signal;

[0011] The ±3rd order diffraction interference grating precision displacement sensor module in the above-mentioned multi-order diffraction grating precision displacement sensor is used to obtain the second interference signal;

[0012] The first interference signal and the second interference signal are processed respectively to obtain the first displacement and the second displacement.

[0013] The final displacement is calculated based on the noise levels of the first displacement, second displacement, ±2nd order diffraction interference grating precision displacement sensor module, and ±3rd order diffraction interference grating precision displacement sensor module.

[0014] According to the specific embodiments provided in this application, this application has the following technical effects:

[0015] 1. This application provides a multi-order diffraction grating precision displacement sensor, which utilizes the polarization characteristics of light to improve the utilization rate of effective light, reduce the interference of ambient stray light on the measurement signal, and improve the accuracy and stability of the overall system.

[0016] 2. The ±2nd order diffraction interference grating precision displacement sensor module and the ±3rd order diffraction interference grating precision displacement sensor module are independent of each other and do not affect each other. The two modules share a single grating, resulting in a compact structure and high space utilization.

[0017] 3. This application uses different noise levels to weight the measurement results of the ±2nd order diffraction interference grating precision displacement sensor module and the ±3rd order diffraction interference grating precision displacement sensor module to obtain the final displacement, thus ensuring that the measurement results are more accurate. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 A schematic diagram of the structure of a multi-order diffraction grating precision displacement sensor provided in an embodiment of this application;

[0020] Figure 2 This is a schematic diagram of the optical path for ±2nd order diffraction.

[0021] Figure 3 This is a schematic diagram of the optical path for ±3rd order diffraction. Detailed Implementation

[0022] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0023] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] In one exemplary embodiment, a multi-order diffraction grating precision displacement sensor is provided, which adopts a symmetrical Littrow optical path structure, with the left and right paths being ±2nd order diffraction optical paths and ±3rd order diffraction optical paths, respectively, and the overall structure is simple and compact.

[0025] like Figure 1 As shown, the multi-order diffraction grating precision displacement sensor includes: a laser 1, a half-wave plate 2, a first non-polarizing beam splitter prism 301, a ±2nd order diffraction interference grating precision displacement sensor module, and a ±3rd order diffraction interference grating precision displacement sensor module.

[0026] The ±2nd order diffraction interference grating precision displacement sensor module includes: a second unpolarized beam splitter 302, a first polarized beam splitter 401, a first quarter-wave plate 501, a second quarter-wave plate 502, a third quarter-wave plate 503, a first reflector 601, a second reflector 602, a grating 7, a first polarizer 801, a second polarizer 802, a first photodetector 901, and a second photodetector 902.

[0027] The ±3rd order diffraction interference grating precision displacement sensor module includes: a third unpolarized beam splitter 303, a second polarized beam splitter 402, a fourth quarter-wave plate 504, a fifth quarter-wave plate 505, a sixth quarter-wave plate 506, a third reflector 603, a fourth reflector 604, a grating 7, a third polarizer 803, a fourth polarizer 804, a third photodetector 903, and a fourth photodetector 904.

[0028] Figure 2 The ±2nd order diffraction optical path for the ±2nd order diffraction interference grating precision displacement sensor module is as follows:

[0029] The emitted light from the laser 1 passes through the half-wave plate 2 and is incident on the first unpolarized beam splitter 301; the beam emitted from the first unpolarized beam splitter 301 is incident on the first polarized beam splitter 401 and splits into two polarized beams of equal intensity.

[0030] The first polarized light beam is reflected by the first mirror 601 after passing through the second quarter-wave plate 502, and is incident on the grating 7 at a Littrow angle. After diffraction on the surface of the grating 7, a +2nd order diffracted beam is obtained. The +2nd order diffracted beam passes through the first mirror 601, the second quarter-wave plate 502 and the first polarizing beam splitter 401 in sequence to obtain the first diffracted light.

[0031] The second polarized light beam is reflected by the second mirror 602 after passing through the third quarter-wave plate 503, and is incident on the grating 7 at a Littrow angle. After diffraction on the surface of the grating 7, it becomes a -2nd order diffracted beam. The -2nd order diffracted beam passes sequentially through the second mirror 602, the third quarter-wave plate 503 and the first polarizing beam splitter 401 to obtain the second diffracted light.

[0032] The first diffracted light and the second diffracted light are combined by the first polarizing beam splitter 401 and emitted together. After passing through the first quarter-wave plate 501, they are incident on the second unpolarizing beam splitter 302 and are split by the second unpolarizing beam splitter 302 to obtain an interference beam.

[0033] The interference beams, after passing through the first polarizer 801 and the second polarizer 802, are received by the first photodetector 901 and the second photodetector 902. In the first photodetector 901 and the second photodetector 902, the +2nd order diffraction beam interferes with the -2nd order diffraction beam to form a first interference signal. The first interference signal is processed to achieve displacement measurement.

[0034] Figure 3 The ±3rd order diffraction optical path for the ±3rd order diffraction interference grating precision displacement sensor module is as follows:

[0035] The emitted light from the laser 1 passes through the half-wave plate 2 and is incident on the first unpolarized beam splitter 301; the beam emitted from the first unpolarized beam splitter 301 is incident on the second polarized beam splitter 402 and splits into two polarized beams of equal intensity.

[0036] The first polarized light is reflected by the third mirror 603 after passing through the fourth quarter-wave plate 504, and is incident on the grating 7 at a Littrow angle. After diffraction on the surface of the grating 7, a +3rd order diffracted beam is obtained. The +3rd order diffracted beam passes sequentially through the third mirror 603, the fourth quarter-wave plate 504 and the second polarizing beam splitter 402 to obtain the third diffracted light.

[0037] The second polarized light beam is reflected by the fourth mirror 604 after passing through the fifth quarter-wave plate 505, and is incident on the grating 7 at a Littrow angle. After diffraction on the surface of the grating 7, it becomes a -3rd order diffracted beam. The -3rd order diffracted beam passes sequentially through the fourth mirror 604, the fifth quarter-wave plate 505, and the second polarizing beam splitter 402 to become a fourth diffracted beam.

[0038] The third diffracted light and the fourth diffracted light are combined by the second polarizing beam splitter 402 and emitted together. After passing through the sixth quarter-wave plate 506, they are incident on the third unpolarizing beam splitter 303. The beam is split by the third unpolarizing beam splitter 303 to obtain an interference beam.

[0039] The interference beams are received by the third photodetector 903 and the fourth photodetector 904 after passing through the third polarizer 803 and the fourth photodetector 904, respectively; in the third photodetector 903 and the fourth photodetector 904, the +3rd order diffraction beam interferes with the -3rd order diffraction beam to form a second interference signal.

[0040] In this implementation, the Littrow angle in the ±2nd order diffraction path is different from that in the ±3rd order diffraction path.

[0041] In one specific embodiment, the laser 1 is a single-frequency laser. The grating 7 is a reflective holographic diffraction grating.

[0042] In one specific embodiment, the polarization angles of the first polarizer 801, the second polarizer 802, the third polarizer 803, and the fourth polarizer 804 are all 45 degrees.

[0043] The aforementioned multi-order diffraction grating precision displacement sensor can simultaneously receive multiple photoelectric signals of different orders. Its diffraction order is not limited to ±2nd order and ±3rd order, but can be ±m order.

[0044] In one exemplary embodiment, a displacement measurement method is provided, specifically including the following steps:

[0045] S1: The first interference signal is obtained by using the ±2nd order diffraction interference grating precision displacement sensor module in the above-mentioned multi-order diffraction grating precision displacement sensor.

[0046] S2: The ±3rd order diffraction interference grating precision displacement sensor module in the above-mentioned multi-order diffraction grating precision displacement sensor obtains the second interference signal.

[0047] S3: Process the first interference signal and the second interference signal respectively to obtain the first displacement and the second displacement.

[0048] S4: Calculate the final displacement based on the noise levels of the first displacement, the second displacement, the ±2nd order diffraction interference grating precision displacement sensor module, and the ±3rd order diffraction interference grating precision displacement sensor module.

[0049] Specifically, the multi-level grating precision displacement sensor is based on the grating diffraction interference effect, when the laser emits a wavelength of... Monochromatic light, at an angle of incidence Incident to grating pitch is When the light is applied to the surface of the grating, multiple diffraction orders will be generated. Let the diffraction angle of the m-th order diffraction be θ. Then the geometric relationships between the incident light, the diffracted light, and the grating satisfy the grating equation:

[0050]

[0051] Where m is the diffraction order, represented by an integer representing the order of the diffracted light.

[0052] During displacement measurement, the motion of the grating along its vector direction introduces the Doppler effect. When the grating 7 moves at a velocity ν along the grating vector direction, let the frequency of the incident light be... The frequency of ±m order diffracted light is and The frequency difference of ±m-order diffracted light can be expressed as:

[0053]

[0054] By combining the ±m-order diffracted beams generated by the grating using optical elements, high-precision measurement of the grating displacement can be achieved based on the principle of difference-frequency interference. When these two diffracted beams meet in space, interference occurs, forming interference fringes. Therefore, when the grating moves a displacement s at a velocity v within a time interval t, the phase change of the interference signal can be expressed as:

[0055]

[0056] As can be seen from the above formula, for every 1 / 2 grating pitch displacement of the grating, the signal phase changes by 2π, that is, the grating pitch is the measurement reference of the grating displacement system.

[0057] According to the above formula, the ±2nd order diffraction interference precision grating sensor can measure the displacement as follows: The ±3rd order diffraction interferometry precision grating sensor in this embodiment can measure displacement as Assume the noise level of the ±2nd order diffraction interferometry precision grating sensor is... The noise level of the ±3rd order diffraction interferometry precision grating sensor is The final displacement is:

[0058] .

[0059] The displacement result is calculated by weighting the noise levels of the two devices, which improves the reliability and accuracy of the displacement result measured by the grating precision displacement sensor.

[0060] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0061] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A grating precision displacement sensor with multi-order diffraction, characterized in that, include: Laser, half-wave plate, first unpolarized beam splitter prism, ±2nd order diffraction interference grating precision displacement sensor module and ±3rd order diffraction interference grating precision displacement sensor module; The ±2nd order diffraction interference grating precision displacement sensor module includes: a second unpolarized beam splitter, a first polarized beam splitter, a first quarter-wave plate, a second quarter-wave plate, a third quarter-wave plate, a first mirror, a second mirror, a grating, a first polarizer, a second polarizer, a first photodetector, and a second photodetector. The ±3rd order diffraction interference grating precision displacement sensor module includes: a third unpolarized beam splitter, a second polarized beam splitter, a fourth quarter-wave plate, a fifth quarter-wave plate, a sixth quarter-wave plate, a third mirror, a fourth mirror, a grating, a third polarizer, a fourth polarizer, a third photodetector, and a fourth photodetector. The ±2nd order diffraction optical path of the ±2nd order diffraction interference grating precision displacement sensor module is as follows: The laser beam emitted from the laser passes through the half-wave plate and is incident on the first unpolarized beam splitter; the beam emitted from the first unpolarized beam splitter is incident on the first polarized beam splitter and splits into two polarized beams of equal intensity. The first polarized light beam is reflected by the first mirror after passing through the second quarter-wave plate and is incident on the grating at a Littrow angle. After diffraction on the surface of the grating, it becomes a +2nd order diffracted beam. The +2nd order diffracted beam passes sequentially through the first mirror, the second quarter-wave plate and the first polarizing beam splitter to obtain the first diffracted light. The second polarized light beam is reflected by the second mirror after passing through the third quarter-wave plate, and is incident on the grating at a Littrow angle. After diffraction on the surface of the grating, it becomes a -2nd order diffracted beam. The -2nd order diffracted beam passes sequentially through the second mirror, the third quarter-wave plate, and the first polarizing beam splitter to obtain the second diffracted light. The first diffracted light and the second diffracted light are combined by the first polarizing beam splitter and emitted together. After passing through the first quarter-wave plate, they are incident on the second unpolarizing beam splitter and are split by the second unpolarizing beam splitter to obtain an interference beam. The interference beams are received by the first photodetector and the second photodetector after passing through the first polarizer and the second polarizer, respectively; in the first photodetector and the second photodetector, the +2nd order diffraction beam interferes with the -2nd order diffraction beam to form a first interference signal; The ±3rd order diffraction optical path of the ±3rd order diffraction interference grating precision displacement sensor module is as follows: The laser beam emitted from the laser passes through the half-wave plate and is incident on the first unpolarized beam splitter; the beam emitted from the first unpolarized beam splitter is incident on the second polarized beam splitter and split into two polarized beams of equal intensity. The first polarized light is reflected by the third mirror after passing through the fourth quarter-wave plate and is incident on the grating at a Littrow angle. After diffraction on the surface of the grating, it becomes a +3rd order diffracted beam. The +3rd order diffracted beam passes sequentially through the third mirror, the fourth quarter-wave plate, and the second polarizing beam splitter to become the third diffracted light. The second polarized light beam is reflected by the fourth mirror after passing through the fifth quarter-wave plate, and is incident on the grating at a Littrow angle. After diffraction on the surface of the grating, it becomes a -3rd order diffracted beam. The -3rd order diffracted beam passes sequentially through the fourth mirror, the fifth quarter-wave plate, and the second polarizing beam splitter to become the fourth diffracted light. The third diffracted light and the fourth diffracted light are combined by the second polarizing beam splitter and emitted together. After passing through the sixth quarter-wave plate, they are incident on the third unpolarizing beam splitter; the beam is split by the third unpolarizing beam splitter to obtain an interference beam. The interference beams are received by the third and fourth photodetectors after passing through the third and fourth polarizers, respectively; in the third and fourth photodetectors, the +3rd order diffraction beams interfere with the -3rd order diffraction beams to form a second interference signal.

2. The multi-order diffraction grating precision displacement sensor according to claim 1, characterized in that, The Littrow angles of the ±2nd order diffraction light path of the ±2nd order diffraction interference grating precision displacement sensor module and the ±3rd order diffraction light path of the ±3rd order diffraction interference grating precision displacement sensor module are different.

3. The multi-order diffraction grating precision displacement sensor according to claim 1, characterized in that, The grating is a reflective holographic diffraction grating.

4. The multi-order diffraction grating precision displacement sensor according to claim 1, characterized in that, The laser is a single-frequency laser.

5. The multi-order diffraction grating precision displacement sensor according to claim 1, characterized in that, The polarization angles of the first polarizer, the second polarizer, the third polarizer, and the fourth polarizer are all 45 degrees.

6. The multi-order diffraction grating precision displacement sensor according to claim 1, characterized in that, When the laser emits a wavelength of Monochromatic light, at an angle of incidence Incident to grating pitch is When the incident light is on the grating surface, multiple diffraction orders will be generated. The geometric relationship between the incident light, the diffracted light, and the grating satisfies the grating equation: in, The grating pitch is the grating pitch. Let be the angle of incidence of the incident light. Let be the diffraction angle of the m-th order diffracted light. Where is the wavelength of the incident light. This refers to the diffraction order.

7. A displacement measurement method, characterized in that, include: The first interference signal is obtained by using the ±2nd order diffraction interference grating precision displacement sensor module in the multi-order diffraction grating precision displacement sensor according to any one of claims 1-6; The second interference signal is obtained by using the ±3rd order diffraction interference grating precision displacement sensor module in the multi-order diffraction grating precision displacement sensor according to any one of claims 1-6; The first interference signal and the second interference signal are processed respectively to obtain the first displacement and the second displacement; The final displacement is calculated based on the noise levels of the first displacement, second displacement, ±2nd order diffraction interference grating precision displacement sensor module, and ±3rd order diffraction interference grating precision displacement sensor module.

8. The displacement measurement method according to claim 7, characterized in that, The final displacement The calculation formula is: in, For the first displacement, For the second displacement, The noise level of the ±2nd order diffraction interference grating precision displacement sensor module. The noise level of the ±3rd order diffraction interference grating precision displacement sensor module.

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