In-plane and out-of-plane two-degree-of-freedom displacement synchronous measurement method and system

Abstract

The application provides a method and system for in-plane and out-of-plane two-degree-of-freedom displacement synchronous measurement, and relates to the field of optical measurement.The technical points are as follows: the light beam emitted by a modulated light source is split into a first light beam and a second light beam by a splitting device;the first light beam enters an F-P cavity formed by a first cavity mirror and a grating to form a first interference light beam after passing through a first ring device;the first interference light beam is received by a first photodetector after sequentially passing through the first cavity mirror and the first ring device;the second light beam enters the F-P cavity formed by a second cavity mirror and the grating to form a second interference light beam after passing through a second ring device;the second interference light beam is received by a second photodetector after sequentially passing through the second cavity mirror and the second ring device;two interference signals are demodulated by a signal processing module to obtain two multi-beam interference phases, and the in-plane and out-of-plane two-degree-of-freedom displacement information of the grating is decoupled.Compared with the prior art, the complexity of the optical path is reduced, the range of the out-of-plane displacement of the grating is improved, and the working distance limit is broken.

Description

Technical Field

[0001] The present application relates to the field of optical measurement technology, and in particular to a method and system for synchronously measuring in-plane and out-of-plane two-degree-of-freedom displacements. Background Art

[0002] Grating interferometer is an effective means for synchronous measurement of two-degree-of-freedom displacement in-plane and out-plane. Its measurement principle is: the Doppler frequency shift generated by the grating in-plane motion and the change in optical path length caused by the out-plane motion jointly lead to the phase change of the interference signal. By measuring the above two parts of the interference signal respectively, the two-degree-of-freedom displacement information of the grating (42) in-plane and out-plane can be decoupled and obtained. For example, double-beam interferometry or multi-beam interferometry commonly used in the prior art, however, the double-beam grating interferometer in the prior art usually has the defects of complex structure, high processing cost, great difficulty in assembly and adjustment, and is not conducive to the miniaturization design of the sensor head and is not conducive to meeting the demand for miniaturization of high-end equipment. The multi-beam grating interferometer simplifies the probe structure to a certain extent, but uses the transmission signal of the multi-beam grating interference, which limits the measurement range of the grating out-plane displacement and also limits the working distance (i.e., the distance between the sensor head and the grating). There are still certain deficiencies in the structure. Summary of the Invention

[0003] The present application provides a method and system for synchronously measuring in-plane and out-of-plane two-degree-of-freedom displacements, which has the advantages of simple structure, convenient installation and adjustment, and flexible working distance, and the probe does not limit the range of the two measured degrees of freedom.

[0004] To achieve the above-mentioned purpose, the first aspect of the present application provides a method for synchronously measuring in-plane and out-of-plane two-degree-of-freedom displacements, wherein a light source modulated by an output signal of a modulation module emits a light beam, which is sequentially split by a light splitting device;

[0005] The first light beam output by the optical splitter passes through the first circulator, generating a first incident light, which enters the FP cavity formed by the first cavity mirror and the grating. The generated first interference light beam passes through the first cavity mirror and the first circulator in sequence and is received by the first photodetector.

[0006] The second light beam output by the optical splitter passes through the second circulator, generating a second incident light, which enters another FP cavity formed by the second cavity mirror and the grating. The generated second interference light beam passes through the second cavity mirror and the second circulator in sequence and is received by the second photodetector.

[0007] The first interference signal received by the first photodetector and the second interference signal received by the second photodetector are transmitted to the signal processing module, and are demodulated by the signal processing module to obtain the first multi-beam interference phase and the second multi-beam interference phase, which are further decoupled to obtain the two-degree-of-freedom displacement information in and out of the grating plane.

[0008] In some embodiments of the first aspect, the first cavity mirror and the second cavity mirror are reflective spectrometers, refractive spectrometers, or diffractive spectrometers.

[0009] In some embodiments of the first aspect, the optical axes of the first incident light and the second incident light form a +m-order or -m-order Littrow angle with the grating normal, where m is a positive integer greater than or equal to 1; or

[0010] The optical axes of the first incident light and the second incident light are parallel to the grating normal; or

[0011] The optical axes of the first incident light and the second incident light are neither parallel to the grating normal nor at any order of Littrow angle.

[0012] In some embodiments of the first aspect, a light deflection device is placed between the first circulating device, the second circulating device and the grating so that the optical axes of the first incident light and the second incident light form a +m-order or -m-order Littrow angle with the grating normal, where m is a positive integer greater than or equal to 1.

[0013] In some embodiments of the first aspect, the light deflecting device includes one or more deflecting devices.

[0014] The second aspect of the present application provides an in-plane and out-of-plane two-degree-of-freedom displacement synchronous measurement system, including a modulation module, a light source, a spectrometer, a first circulator, a second circulator, a first cavity mirror, a second cavity mirror, a grating, a first photoelectric detection module, a second photoelectric detection module, and a signal processing module:

[0015] The first cavity mirror and the grating, the second cavity mirror and the grating respectively form an FP cavity;

[0016] The light source modulated by the modulation module emits a light beam, which is split by the optical splitter;

[0017] The first light beam output by the optical splitter passes through the first circulator, generating a first incident light, which enters the FP cavity formed by the first cavity mirror and the grating. The generated first interference light beam passes through the first cavity mirror and the first circulator in sequence and is received by the first photodetector.

[0018] The second light beam output by the optical splitter passes through the second circulator, generating a second incident light, which enters the FP cavity formed by the second cavity mirror and the grating. The generated second interference light beam passes through the second cavity mirror and the second circulator in sequence and is received by the second photodetector.

[0019] The first interference signal received by the first photodetector and the second interference signal received by the second photodetector are transmitted to the signal processing module, and the first multi-beam interference phase and the second multi-beam interference phase are obtained by demodulation by the signal processing module, and the two-degree-of-freedom displacement information in and out of the grating plane is obtained by decoupling.

[0020] In some embodiments of the second aspect, the first incident light output by the first circulator forms a spatial transmission light path through the first collimator and then enters the first FP cavity; and / or,

[0021] The second incident light output by the second circulatory device passes through the second collimating device to form a spatial transmission light path and then enters the second FP cavity.

[0022] In some embodiments of the second aspect, the first cavity mirror is integrated on the light-emitting surface of the first collimating device by bonding, coating, mechanical scratching or photolithography; and / or,

[0023] The second cavity mirror is integrated on the light-emitting surface of the second collimating device by bonding, coating, mechanical scratching or photolithography.

[0024] In some embodiments of the second aspect, the optical axis of the spatial transmission light path entering the first FP cavity is perpendicular to the first cavity mirror and forms a +m or -m order Littrow angle with the grating normal, where m is a positive integer greater than or equal to 1; and / or,

[0025] The optical axis of the spatial light path entering the second FP cavity is perpendicular to the second cavity mirror and forms a +m or -m order Littrow angle with the grating normal, where m is a positive integer greater than or equal to 1.

[0026] In some embodiments of the second aspect, the light beam emitted by the light source passes through an optical isolator before entering the optical splitter; and / or,

[0027] At least one light deflecting device is located between the first cavity mirror, the second cavity mirror and the grating.

[0028] This application has the following beneficial effects:

[0029] Compared with the dual-beam grating interference scheme in the existing technology, it effectively reduces the complexity of the optical path, reduces the difficulty of miniaturization design, and reduces the difficulty and cost of processing and assembly; compared with the multi-beam grating interference scheme in the existing technology, it effectively improves the range of grating out-of-plane displacement, and at the same time breaks through the limitation of the photodetector image plane size on the working distance. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0031] Figure 1 This is a schematic diagram of the connection structure of each module in a synchronous measurement system for in-plane and out-of-plane two-degree-of-freedom displacements in an embodiment of the present application;

[0032] Figure 2 This is a schematic structural diagram of the connection between the collimating device and the cavity mirror in Example 1 of the present application;

[0033] Figure 3 This is a schematic diagram of the structure of the connection between the collimating device and the cavity mirror in the second embodiment of the present application;

[0034] Figure 4 This is a structural diagram of the connection between the collimating device and the cavity mirror in Example 3 of the present application.

[0035] Reference numerals:

[0036] 1. Circuit part; 11. Modulation module; 12. Signal processing module; 2. Light source; 3. Transmission optical path; 31. Optical splitter; 32a. First circulating device; 32b. Second circulating device; 33a. First collimator; 33b. Second collimator; 4. Fabry-Perot cavity; 41a. First cavity mirror; 41b. Second cavity mirror; 42. Grating; 5a. First photodetector; 5b. Second photodetector; 6a. First light deflection device; 6b. Second light deflection device. DETAILED DESCRIPTION

[0037] The implementation methods of the present application are further described in detail below in conjunction with the drawings and examples. The terms used in the implementation methods of the present application are only used to explain the specific examples of the present application and are not intended to limit the present application.

[0038] In the prior art, simultaneous measurement methods for in-plane and out-of-plane two-degree-of-freedom displacements are mostly based on the principle of dual-beam interferometry. For example, the public document with announcement number CN109579694B discloses a high-tolerance two-degree-of-freedom heterodyne grating interferometry measurement method and system. The dual-beam interferometry principle utilizes a reference interference beam, a first measurement beam, and a second measurement beam to obtain the grating's two-degree-of-freedom displacement information through phase decoupling operations on the three interfering beams. However, dual-beam grating interferometry solutions are complex in structure, expensive to manufacture, and difficult to assemble and adjust, hindering the miniaturization of sensor heads and failing to meet the demands for miniaturized, embedded grating interferometry in high-end equipment.

[0039] Another approach utilizes the principle of transmissive multi-beam grating interferometry. For example, the public document CN112444194B discloses a Fabry-Perot grating interferometer for two-degree-of-freedom displacement measurement, its measurement method, and a six-degree-of-freedom interferometer. The multi-beam interferometry is embodied in that the incident light emitted by a laser light source enters the grating at the Littrow angle, forming a self-collimating optical path structure and causing diffraction on the grating surface. A Fabry-Perot cavity (FP cavity) is formed between the partially transmissive surface and the grating. The phase of the transmission signal formed by the multi-beam grating interferometry between the two FP cavities is detected, and further decoupling is performed to obtain the two-degree-of-freedom displacement information. While the transmissive multi-beam grating interferometry approach simplifies the probe structure to a certain extent, the use of the transmission signal of the multi-beam grating interferometry limits the measurement range of the grating's out-of-plane displacement and also restricts the working distance (i.e., the distance between the sensing probe and the grating). Therefore, certain structural deficiencies still exist.

[0040] like Figure 1 As shown, in order to solve the above technical problems in the prior art, the embodiment of the present application provides an in-plane and out-of-plane two-degree-of-freedom displacement synchronous measurement system, including a circuit part 1, a light source 2, a transmission optical path 3, a Fabry-Perot cavity 4, and a photodetector;

[0041] The optical path part 1 includes a modulation module 11 and a signal processing module 12 connected to each other;

[0042] The transmission optical path 3 includes a splitter 31, a first circulator 32a, and a second circulator 32b. The splitter 31 is connected to the first circulator 32a and the second circulator 32b respectively.

[0043] The Fabry-Perot cavity 4 includes a first cavity mirror 41a, a second cavity mirror 41b, and a grating 42. The grating 42 is connected to the first cavity mirror 41a and the second cavity mirror 41b respectively.

[0044] The photodetector includes a first photodetector 5a and a second photodetector 5b;

[0045] The light source 2 is connected to the modulation module 11 and the optical splitter 31 respectively;

[0046] The first photodetector 5a is connected to the signal processing module 12 and the first circulatory device 32a respectively; the second photodetector 5b is connected to the signal processing module 12 and the second circulatory device 32b respectively;

[0047] The first cavity mirror 41 a is connected to the first circulator 32 a , and the second cavity mirror 41 b is connected to the second circulator 32 b .

[0048] It should be understood that the “connection” in this embodiment can be an indirect connection or a direct connection, and the indirect connection includes an optical path connection.

[0049] The modulation module 11 generates electrical signals for light source modulation and signal demodulation, which are transmitted to the signal processing module 12 and light source 2, respectively. Light source 2 emits modulated laser light, which is then transmitted to the optical splitter 31 for splitting, generating a first light beam and a second light beam. The first and second light beams pass through the first and second circulators 32a and 32b, respectively, forming the first and second incident light beams. These beams then enter the two Fabry-Perot cavities 4 formed by the first and second cavity mirrors 41a and grating 42, and the second and second cavity mirrors 41b and grating 42, respectively, resulting in multi-beam interference. The transmitted signals from the two Fabry-Perot cavities 4 again pass through the first and second cavity mirrors 41a and 41b, respectively, and are redirected by the first and second circulators 32a and 32b before reaching the first and second photodetectors 5a and 5b. The electrical signals generated by the photodetectors are input to the signal processing module 12, where they are resolved to determine the two-degree-of-freedom displacement of the grating 42.

[0050] like Figure 2 As shown, in the first embodiment of the present application, the optical splitter 31 is a fiber beam splitter, the first circulator 32a and the second circulator 32b are fiber circulators, the first cavity mirror 41a and the second cavity mirror 41b are semi-reflective and semi-transparent, and the in-plane and out-of-plane two-degree-of-freedom displacement synchronous measurement system also includes a first collimator 33a and a second collimator 33b, which are respectively integrated on the light-emitting surfaces of the first collimator 33a and the second collimator 33b by coating. The light beam output by the collimator forms a Littrow angle with the grating 42.

[0051] like Figure 3 As shown, in embodiment 2 of the present application, the first collimator 33a and the second collimator 33b are placed vertically to the grating 42, the first cavity mirror 41a and the second cavity mirror 41b are semi-reflective and semi-mirror, and are respectively integrated on the light-emitting surfaces of the first collimator 33a and the second collimator 33b by coating. The in-plane and out-of-plane two-degree-of-freedom displacement synchronous measurement system also includes a first optical path deflection element 6a and a second optical path deflection element 6b. The first optical path deflection element 6a and the second optical path deflection element 6b are added to the Fabry-Perot cavity 4 so that the light beam output by the collimator is at a Littrow angle with the grating 42.

[0052] like Figure 4 As shown, in embodiment three of the present application, the first collimating device 33a and the second collimating device 33b are placed perpendicular to the grating 42, and the first cavity mirror 41a and the second cavity mirror 41b are transmission gratings, which are directly engraved on the light-emitting surfaces of the first collimating device 33a and the second collimating device 33b, so that the light beam output by the collimating device is at a Littrow angle with the grating 42.

[0053] The working principle of the in-plane and out-of-plane two-degree-of-freedom displacement synchronous measurement system provided in the embodiments of the present application is as follows: assuming that the in-plane direction motion displacement of the grating 42 is x and the out-of-plane direction motion displacement is z; the displacement corresponding to the phase of the multi-beam interference signal obtained by the first photodetector 5a can be expressed as x+kz (the coefficient k is a constant determined by the optical path Littrow angle); the displacement corresponding to the phase of the multi-beam interference signal obtained by the second photodetector 5b is x-kz, so that the displacement information in two directions can be obtained by signal processing module 12.

[0054] In combination with Figures 1 to 4 As shown in the drawings, the embodiments of the present application also provide an in-plane and out-of-plane two-degree-of-freedom displacement synchronous measurement method, the light source 2 emits a light beam modulated by the output signal of the modulation module 1, and the light beam is sequentially split by the light splitting device 31;

[0055] The first light beam output by the light splitting device 31 passes through the first loop device 32a to generate first incident light, which enters the F-P cavity (first F-P cavity) composed of the first cavity mirror 41a and the grating 42, and the generated first interference light beam sequentially passes through the first cavity mirror 41a and the first loop device 32a and is received by the first photodetector 5a;

[0056] The second light beam output by the light splitting device 31 passes through the second loop device 32b to generate second incident light, which enters another F-P cavity (second F-P cavity) composed of the second cavity mirror 41b and the grating 42, and the generated second interference light beam sequentially passes through the second cavity mirror 41b and the second loop device 32b and is received by the second photodetector 5b;

[0057] The first interference signal received by the first photodetector 5a and the second interference signal received by the second photodetector 5b are transmitted to the signal processing module 12, and the first multi-beam interference phase and the second multi-beam interference phase are obtained by demodulation of the signal processing module 12, and the in-plane and out-of-plane two-degree-of-freedom displacement information of the grating 42 is further decoupled.

[0058] In some embodiments of the present embodiment, the first cavity mirror 41a and the second cavity mirror 41b are reflective light splitting devices, refractive light splitting devices or diffractive light splitting devices.

[0059] In some embodiments of the present embodiment, the optical axis of the first incident light and the second incident light forms a +mth order or -mth order Littrow angle with the normal line of the grating 42, where m is a positive integer greater than or equal to 1; or,

[0060] The optical axis of the first incident light and the second incident light is parallel to the normal line of the grating 42; or,

[0061] The optical axis of the first incident light and the second incident light is neither parallel to the normal line of the grating 42 nor forms any order Littrow angle.

[0062] In some implementations of this embodiment, a light deflection device is placed between the first circulator 32a, the second circulator 32b and the grating 42 so that the optical axes of the first incident light and the second incident light form a +m-order or -m-order Littrow angle with the normal of the grating 42, where m is a positive integer greater than or equal to 1.

[0063] In some implementations of this embodiment, the light deflecting device includes one or more deflecting devices, for example, a first light deflecting device 6a and a second light deflecting device 6b.

[0064] The method and system for synchronously measuring both in-plane and out-of-plane displacements of two degrees of freedom provided in the embodiments of the present application have the advantages of simple structure, easy installation and adjustment, and flexible working distance, and the probe does not impose any restrictions on the range of either measured degree of freedom. Compared with existing dual-beam grating interferometry technology, this method effectively reduces the complexity of the optical path, the difficulty of miniaturization design, and the difficulty and cost of processing and installation. Compared with existing multi-beam grating interferometry technology, it effectively increases the range of grating out-of-plane displacement, while also breaking through the limitation of the photodetector image plane size on the working distance.

[0065] In the description of the embodiments of the present application, it should be noted that "and / or" is merely a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent three situations: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this document generally indicates that the objects associated before and after are in an "or" relationship. Terms such as "include" and / or "have" may be interpreted as indicating specific characteristics, numbers, operations, constituent elements, components, or combinations thereof, but may not be interpreted as excluding the existence or possibility of adding one or more other characteristics, numbers, operations, constituent elements, components, or combinations thereof.

[0066] In the description of the embodiments of this application, it should be noted that the terms "first," "second," etc. are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly specifying the number of the technical features indicated. Features specified as "first" or "second" may explicitly or implicitly include one or more of the features. Unless otherwise specified, "plurality" means two or more.

[0067] The above embodiments are merely explanations of the present application and are not limitations of the present application. After reading this specification, those skilled in the art may make modifications to the implementation methods of the present application as needed without any creative contribution. However, as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A method for synchronously measuring in-plane and out-of-plane two-degree-of-freedom displacements, characterized in that: The light source (2) modulated by the output signal of the modulation module (11) emits a light beam, which is sequentially split by the light splitting device (31); The first light beam output by the optical splitter (31) passes through the first circulator (32a), generating a first incident light, which enters the FP cavity formed by the first cavity mirror (41a) and the grating (42). The generated first interference light beam passes through the first cavity mirror (41a) and the first circulator (32a) in sequence, and is received by the first photodetector (5a); The second light beam output by the optical splitter (31) passes through the second circulator (32b), generating a second incident light, which enters another FP cavity formed by the second cavity mirror (41b) and the grating (42). The generated second interference light beam passes through the second cavity mirror (41b) and the second circulator (32b) in sequence, and is received by the second photodetector (5b); The first interference signal received by the first photodetector (5a) and the second interference signal received by the second photodetector (5b) are transmitted to a signal processing module (12), demodulated by the signal processing module (12) to obtain a first multi-beam interference phase and a second multi-beam interference phase, and further decoupled to obtain two-degree-of-freedom displacement information of the grating (42) in-plane and out-of-plane; The optical axes of the first incident light and the second incident light form a +m-order or -m-order Littrow angle with the normal of the grating (42), where m is a positive integer greater than or equal to 1; or The optical axes of the first incident light and the second incident light are parallel to the normal line of the grating (42); or The optical axes of the first incident light and the second incident light are neither parallel to the normal of the grating (42) nor present any order of Littrow angle; A light deflection device is placed between the first circulatory device (32a), the second circulatory device (32b) and the grating (42) so that the optical axes of the first incident light and the second incident light form a +m-order or -m-order Littrow angle with the normal of the grating (42), where m is a positive integer greater than or equal to 1.

2. The method for synchronously measuring in-plane and out-of-plane two-degree-of-freedom displacement according to claim 1, characterized in that: The first cavity mirror (41a) and the second cavity mirror (41b) are reflective spectrometers, refractive spectrometers or diffraction spectrometers.

3. The method for synchronously measuring in-plane and out-of-plane two-degree-of-freedom displacements according to claim 1, characterized in that: The light deflecting device includes one or more deflecting devices.

4. A synchronous measurement system for in-plane and out-of-plane two-degree-of-freedom displacements applicable to the method of any one of claims 1 to 3, characterized in that: The invention comprises a modulation module (11), a light source (2), a spectrometer (31), a first circulator (32a), a second circulator (32b), a first cavity mirror (41a), a second cavity mirror (41b), a grating (42), a first photodetector (5a), a second photodetector (5b), and a signal processing module (12): The first cavity mirror (41a) and the grating (42), and the second cavity mirror (41b) and the grating (42) respectively form an FP cavity; The light source (2) modulated by the modulation module (11) emits a light beam, which is split by the light splitting device (31); The first light beam output by the optical splitter (31) passes through the first circulator (32a), generating a first incident light, which enters the FP cavity formed by the first cavity mirror (41a) and the grating (42). The generated first interference light beam passes through the first cavity mirror (41a) and the first circulator (32a) in sequence, and is received by the first photodetector (5a); The second light beam output by the optical splitter (31) passes through the second circulator (32b), generating a second incident light, which enters the FP cavity formed by the second cavity mirror (41b) and the grating (42). The generated second interference light beam passes through the second cavity mirror (41b) and the second circulator (32b) in sequence, and is received by the second photodetector (5b); The first interference signal received by the first photodetector (5a) and the second interference signal received by the second photodetector (5b) are transmitted to a signal processing module (12), demodulated by the signal processing module (12) to obtain a first multi-beam interference phase and a second multi-beam interference phase, and decoupled to obtain two-degree-of-freedom displacement information of the grating (42) in-plane and out-of-plane; The first incident light output by the first circulatory device (32a) passes through the first collimating device (33a) to form a spatial transmission light path and then enters the first FP cavity; and / or, The second incident light output by the second circulating device (32b) passes through the second collimating device (33b) to form a spatial transmission light path and then enters the second FP cavity; The first cavity mirror (41a) is integrated on the light-emitting surface of the first collimating device (33a) by bonding, coating, mechanical scratching or photolithography; and / or, The second cavity mirror (41b) is integrated on the light-emitting surface of the second collimating device (33b) by bonding, coating, mechanical scratching or photolithography; The light beam emitted by the light source (2) passes through an optical isolator before entering the optical splitter (31); and / or, At least one light deflection device (6) is present between the first cavity mirror (41a), the second cavity mirror (41b) and the grating (42).

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