WO2020007218A1 - 二自由度外差光栅干涉测量系统 - Google Patents

二自由度外差光栅干涉测量系统 Download PDF

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WO2020007218A1
WO2020007218A1 PCT/CN2019/092922 CN2019092922W WO2020007218A1 WO 2020007218 A1 WO2020007218 A1 WO 2020007218A1 CN 2019092922 W CN2019092922 W CN 2019092922W WO 2020007218 A1 WO2020007218 A1 WO 2020007218A1
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measurement
grating
interference signal
light
beam splitting
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French (fr)
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朱煜
张鸣
王磊杰
杨富中
成荣
李鑫
叶伟楠
胡金春
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Tsinghua University
Beijing U Precision Tech Co Ltd
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Tsinghua University
Beijing U Precision Tech Co Ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02001—Interferometers characterised by controlling or generating intrinsic radiation properties
    • G01B9/02002—Interferometers characterised by controlling or generating intrinsic radiation properties using two or more frequencies
    • G01B9/02003—Interferometers characterised by controlling or generating intrinsic radiation properties using two or more frequencies using beat frequencies
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
    • G01B11/06—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material
    • G01B11/0616—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material of coating
    • G01B11/0641—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material of coating with measurement of polarization
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
    • G01B11/06—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material
    • G01B11/0616—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material of coating
    • G01B11/0675—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material of coating using interferometry
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02015—Interferometers characterised by the beam path configuration
    • G01B9/02027—Two or more interferometric channels or interferometers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02049—Interferometers characterised by particular mechanical design details
    • G01B9/02051—Integrated design, e.g. on-chip or monolithic
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B2290/00—Aspects of interferometers not specifically covered by any group under G01B9/02
    • G01B2290/70—Using polarization in the interferometer

Definitions

  • the invention relates to the technical field of interferometry, and more particularly, to a two-degree-of-freedom heterodyne grating interferometry system.
  • the interferometric measurement system As a typical displacement sensor, the interferometric measurement system has the advantages of length traceability, high measurement accuracy, large measurement range, large dynamic measurement range, easy installation and debugging, etc., and is widely used in precision and ultra-precision measurement fields. Common in precision machinery and processing equipment.
  • interferometry systems can be mainly divided into laser interferometry systems and grating interferometry systems.
  • Laser interferometry systems are based on the principle of laser interference measurement
  • grating interferometry systems are based on the principle of diffraction interference.
  • the measurement basis is the grating pitch. The sensitivity to environmental fluctuations is relatively low, and the accuracy of repeated measurements is higher.
  • the rotation angle error of the grating is unavoidable, resulting in an included angle between the measurement beam and the reference beam, and the coaxial interference cannot be achieved. Therefore, what the detector receives is not an ideal interference spot, but an interference fringe with a certain fringe period, which causes the intensity of the AC signal, that is, the interferometric measurement signal AC / DC ratio to decrease rapidly. A good AC signal strength is the basis for displacement measurement.
  • the rotation angle error of the grating will lead to a reduction in signal strength. When there is a large rotation angle deviation of the grating, the system will not be able to achieve displacement measurement.
  • the existing solutions mainly include introducing a pyramid prism into the optical path to eliminate the angle of the beam, so that the reference beam and the measurement beam in the detector will not form interference fringes.
  • a pyramid prism into the optical path to eliminate the angle of the beam, so that the reference beam and the measurement beam in the detector will not form interference fringes.
  • the present invention proposes a two-degree-of-freedom grating interferometry system with a large rotation angle tolerance.
  • the grating interferometry system of the present invention is particularly suitable for industrial Scenarios with high error requirements can also be applied to precision measurement of displacement of workpiece tables such as precision machine tools, coordinate measuring machines, semiconductor testing equipment, etc.
  • a two-degree-of-freedom grating interferometric measurement system includes: a single-frequency laser 1 for emitting a single-frequency laser, the single-frequency laser can be split into a reference light and a measurement light; an interferometer lens group 3 and a measurement Grating 4 is used to form the reference light and the measurement light into a reference interference signal and a measurement interference signal; a receiving fiber is used to receive the reference interference signal and the measurement interference signal, and the core diameter of the receiving fiber is smaller than the reference interference The interference fringe width of the signal and the measurement interference signal is such that the receiving fiber receives the reference interference signal and a portion of the measurement interference signal.
  • the receiving optical fiber is a multimode optical fiber 5
  • the reference interference signal is one
  • the measurement interference signal is two.
  • the two measurement interference signals and one reference interference signal are passed through the multimode fiber, respectively. 5 Coupling receives and outputs three optical signals.
  • the measurement grating 4 can linearly move in two degrees of freedom horizontally and vertically with respect to the interferometer lens group 3.
  • the interferometer lens group 3 includes: a reflector 35, a refractive element 33, a 1/4 wave plate 34, a beam splitter prism 31, and a polarization beam splitter prism 32 in sequence from one side to the other, wherein the beam splitter prism 31 is located above the polarization beam splitting prism 32.
  • the reference light is divided into three beams after passing through the beam splitting prism 31, and is reflected by the polarization beam splitting prism 32 as reference light for three-way interference signals;
  • the measurement light is divided into three beams after passing through the beam splitting prism 31, and two beams of measurement light are reflected by the polarization beam splitting prism 32 and then pass through the 1/4 wave plate 34 and the refractive element 33 and are incident on the beam.
  • the measurement grating 4 returns after being diffracted by the grating, and transmits again through the polarization beam splitting prism 32, and then interferes with two of the three reference signals of the interference signal to form two measurement interference signals;
  • the polarization beam splitting prism 32 After another beam of measurement light is reflected by the polarization beam splitting prism 32, it first passes through the 1/4 wave plate 34, then is reflected by the mirror 35 and returns along the original optical path, and passes through the 1/4 wave plate 34 again. 2. After transmitting through the polarization beam splitting prism 32, it interferes with another one of the reference light of the three interference signals to form a reference interference signal.
  • the components in the interferometer lens group 3 are closely adjacent and fixed and integrated into an integrated structure.
  • the cross section of the refractive element 33 is an isosceles trapezoid, and the measurement light is refracted when transmitted through both sides of the trapezoid, and reflected when transmitted through the top of the trapezoid.
  • the incident light path reaches the measurement grating 4 at a specific angle, and the specific angle makes the diffracted light path coincide with the incident light path; the diffracted light path passes through The refractive element 33 interferes in parallel with two of the three reference signals of the interference signal to form two measurement interference signals.
  • the interferometry system further includes an acousto-optic modulator 2, and the acousto-optic modulator 2 is configured to shift the frequency of the single-frequency laser beam after the beam splitting.
  • the interferometry system further includes a photoelectric conversion unit 6 and an electronic signal processing unit 7, wherein: the photoelectric conversion unit 6 is configured to receive an optical signal transmitted by the multimode optical fiber 5 and convert the optical signal into an electrical signal for input. To the electronic signal processing component 7; the electronic signal processing component 7 receives the electrical signal, and is used to calculate a linear displacement of the measurement grating 4.
  • the two-degree-of-freedom heterodyne grating interferometry system provided by the present invention has the following advantages:
  • the measuring system of the present invention can effectively avoid the installation error of the angle between the interferometer and the measuring grating and the existing problems during the movement on the basis of meeting the measurement accuracy requirements.
  • the effect of angular deviation on the strength of the measured signal is a simple one-dimensional measurement technique.
  • the measurement system of the present invention has a small volume and a high degree of integration, which effectively improves the space utilization rate and the integration degree of the entire application system.
  • the measurement system can realize two-degree-of-freedom simultaneous measurement including two translational displacements, low environmental sensitivity, easy processing of measurement signals, and resolution and accuracy of nanometers or higher.
  • FIG. 1 is a schematic diagram of a two-degree-of-freedom heterodyne interferometric measurement system according to the present invention
  • FIG. 2 is a schematic structural diagram of an interferometer mirror group according to the present invention.
  • FIG. 3 is a schematic diagram when a grating angle error exists according to the present invention.
  • FIG. 4 is a schematic diagram of a comparison between the receiving fiber in the A-A direction and the interference fringe in FIG. 3.
  • 1 single-frequency laser
  • 2 acousto-optic modulator
  • 3 interferometer mirror group
  • 4 measurement grating
  • 5 multimode fiber
  • 6 photoelectric conversion unit
  • 7 electronic signal processing component
  • 31 spectral Prism
  • 32-polarizing beam splitting prism 32-polarizing beam splitting prism
  • 33-refractive element 34-1 / 4 wave plate, 35-reflector.
  • connection should be understood in a broad sense unless explicitly stated and limited otherwise.
  • they may be fixed connections or removable.
  • Connection, or integral connection it can be mechanical or electrical connection; it can be directly connected, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements.
  • connection, or integral connection it can be mechanical or electrical connection; it can be directly connected, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements.
  • FIG. 1 is a schematic diagram of a two-degree-of-freedom heterodyne grating interferometry system according to the present invention.
  • the two-degree-of-freedom heterodyne grating interferometry system with a large rotation angle tolerance includes a single-frequency laser 1 and an acoustooptic modulation Device 2, interferometer lens group 3, measuring grating 4, receiving fiber, photoelectric conversion unit 6, and electronic signal processing unit 7.
  • the receiving optical fiber is a multi-mode optical fiber 5
  • the measurement grating 4 is a one-dimensional reflective grating.
  • FIG. 2 is a schematic structural diagram of an interferometer lens group according to the present invention.
  • the interferometer lens group 3 is from one side to the other side (from left to right in FIG. 2, or from close to the measurement grating 4). (From one side to the other) includes: a reflector 35, a refractive element 33, a 1/4 wave plate 34, a beam splitter prism 31, and a polarization beam splitter prism 32, wherein the beam splitter prism 31 is located in the polarization beam splitter prism 32 That is, the spectroscopic prism 31 is located on the upper layer of the interferometer mirror group, the polarization beam splitter prism 32 is located on the lower layer of the interferometer mirror group, and the refractive element 33 is located near the top of one side of the interferometer mirror group (near the top of the left side in FIG. 2). To achieve a highly integrated integration, it is preferred that the components in the interferometer mirror group 3 are closely adjacent and fixed, integrated into an integrated structure
  • FIG. 3 is a schematic diagram of a rotation angle error of the grating of the present invention.
  • the measurement light will deviate from the reference light, and there is a certain included angle.
  • the reference light on the detector The two spots of the measurement light will deviate and form interference fringes.
  • the part of the interference light signal is directly received by the multimode fiber 5. It can be seen from FIG. 4 that the core diameter of the multimode fiber 5 is smaller than the width of the interference fringes.
  • the single-frequency laser 1 emits single-frequency light, which is split by the fiber coupling and beam splitter and then incident on the acousto-optic modulator 2 to shift the frequency. After being collimated by the Green lens, two channels of polarized light s light with frequency difference are obtained. One of them is used as reference light and the other is used as measurement light.
  • the reference light passes through the upper beam splitting prism 31 and is split twice to obtain three laser beams, which are incident downward and reflected by the polarizing beam splitting prism as the three-way interference signal reference light.
  • the measurement light passes through the beam splitting prism 31, and three laser beams are also incident downward. Two of them are reflected by the polarization beam splitting prism 32, then pass through the 1/4 wave plate 34, the refractive element 33 is deflected, and then enter the measuring grating 4. After diffraction, the ⁇ 1st-order diffracted light contains the rotation angle and displacement information of the grating, returns along the original optical path, passes through the 1/4 wave plate 34 again, and the polarization beam splitter prism 32 transmits and interferes with the reference light to form two-way measurement interference signals; One measurement light is reflected by the polarization beam splitting prism 32, and then passes through the 1/4 wave plate 34 in turn. After reflection by the mirror 35, it returns along the original optical path. After passing through the 1/4 wave plate 34 again, the polarization beam splitting prism 32 transmits and interferes with the reference light to form Reference interference signal.
  • the light path of the present invention adopts a litro-type arrangement, that is, after the measurement light is deflected by the refractive element 33, the measurement light is incident on the measurement grating 4 at a specific angle, so that the diffracted optical path coincides with the incident optical path, and the diffracted optical path passes through the refractive element.
  • 33 forms the measurement light parallel to the reference light, passes through the 1/4 wave plate 34 again, and the polarization beam splitter prism 32 transmits the interference with the reference light to form two measurement signals.
  • the two measurement interference signals and one reference interference signal are directly coupled to a part of the interference spot through three multi-mode optical fibers 5 respectively to form three signals in total, and their signal strength can meet the measurement requirements.
  • the signal is transmitted to the photoelectric conversion unit 6 to be converted into an electric signal, and is input to the electronic signal processing unit 7 for processing.
  • the obtained phase information is used to solve a two-degree-of-freedom linear motion.
  • the electronic signal processing component 7 outputs a two-degree-of-freedom linear displacement.
  • x and z are the grating displacements
  • ⁇ 1 and ⁇ 2 are the phase changes of the two measurement interference signals relative to the reference interference signal
  • p is the grating pitch
  • ⁇ is the laser wavelength
  • ⁇ is the Littrow angle
  • the measurement system and structural scheme given in the above embodiments can realize the simultaneous measurement of two linear degrees of freedom, and the system has a short measurement optical path and little environmental impact.
  • the use of multimode fiber in the measurement system can effectively reduce the volume and number of system components. To improve the anti-interference ability and system integration of the system, it can effectively avoid the influence of the angular installation error between the interferometer and the measuring grating and the angular deviation during the movement on the strength of the measurement signal.
  • the measurement signal is easy to process and the linear displacement
  • the measurement resolution can reach nm level.
  • the grating interferometer measurement system also has the advantages of simple structure, small size, light weight, easy installation and layout, and convenient application.
  • the two-degree-of-freedom heterodyne grating interferometer displacement measurement system can also be applied to the precision measurement of workpiece table displacements of precision machine tools, coordinate measuring machines, semiconductor testing equipment, and the like.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Instruments For Measurement Of Length By Optical Means (AREA)
  • Length Measuring Devices By Optical Means (AREA)

Abstract

一种二自由度外差光栅干涉测量系统，包括：单频激光器（1），用于发出单频激光，单频激光可分束为一束参考光和一束测量光；干涉仪镜组（3）和测量光栅（4），用于将参考光和测量光形成参考干涉信号和测量干涉信号；接收光纤（5），用于接收参考干涉信号和测量干涉信号，该接收光纤（5）的芯径小于参考干涉信号和测量干涉信号的干涉条纹宽度，使得接收光纤（5）接收参考干涉信号和测量干涉信号的局部。该测量系统对光栅转角误差不敏感、体积小、质量轻、便于布置等优点，特别适用于工业应用中对安装误差要求较高的场景。

Description

二自由度外差光栅干涉测量系统 技术领域
本发明涉及干涉测量技术领域，更具体地，涉及一种二自由度外差光栅干涉测量系统。
背景技术
干涉测量系统作为一种典型的位移传感器具有对长度的可追溯性、测量精度高、测量范围大、动态测量范围大、易于安装和调试等优点，而被广泛应用于精密和超精密测量领域，常见于精密机械和加工设备中。目前干涉测量系统主要可以分为激光干涉测量系统和光栅干涉测量系统，激光干涉测量系统是基于激光干涉的测量原理，而光栅干涉测量系统基于衍射干涉原理，其测量基准为光栅的栅距，对环境波动的敏感性相对较低，重复测量精度更高。
由于安装以及运动过程中的振动等原因，不可避免的存在光栅的转角误差，导致测量光束和参考光束间存在夹角，无法实现共轴干涉。因此，探测器接收到的并非理想的干涉光斑，而是具有一定条纹周期的干涉条纹，造成交流信号的强度即干涉测量信号AC/DC比迅速减小。良好的交流信号强度是实现位移测量的基础，光栅的转角误差将导致信号强度的降低，在光栅存在较大的转角偏差时，系统将无法实现位移的测量。
针对上述问题，目前已有的解决方案主要是在光路中引入角锥棱镜，消除光束夹角，这样在探测器出参考光束和测量光束不会形成干涉条纹。如美国Zygo公司美国专利US20110255096A1(公开日2011年10月20日)，但由于测量光路和参考光路并不重合，仍然存在光束的平行偏离，光栅存在较小转角时，交流信号的AC/DC比下降较小，减轻了光栅转角对测量信号质量的影响，但无法从根本上消除，且由于角锥棱镜的引入，导致光路比较复杂，往往形成二次衍射光路，其能量损失较大。
因此，亟需提供一种能够有效的解决由于测量光栅的安装和运动偏差导 致的测量信号强度降低的问题，降低对光栅安装精度及运动过程中转角偏差的要求，特别适用于工业应用中对安装误差要求较高的场景，并进一步具有光学结构简单紧凑，便于实际安装操作，稳定性及经济性好等特点的光栅干涉测量系统。
发明内容
为解决现有技术中存在的问题和满足本领域技术发展需要，本发明提出一种具有大转角允差的二自由度光栅干涉测量系统，本发明光栅干涉测量系统特别适用于工业应用中对安装误差要求较高的场景，还能应用于精密机床、三坐标测量机、半导体检测设备等工件台位移的精密测量等场合。
本发明所采用的技术方案为：
一种二自由度光栅干涉测量系统，包括：单频激光器1，用于发出单频激光，所述单频激光可分束为一束参考光和一束测量光；干涉仪镜组3和测量光栅4，用于将所述参考光和测量光形成参考干涉信号和测量干涉信号；接收光纤，用于接收所述参考干涉信号和测量干涉信号，所述接收光纤的芯径小于所述参考干涉信号和测量干涉信号的干涉条纹宽度，使得所述接收光纤接收所述参考干涉信号和测量干涉信号的局部。
进一步的，所述接收光纤为多模光纤5，所述参考干涉信号为一路，所述测量干涉信号为两路，所述两路测量干涉信号和一路参考干涉信号，分别经所述多模光纤5耦合接收并输出三路光信号。
进一步的，所述测量光栅4可相对于所述干涉仪镜组3做水平向和垂向两个自由度的线性运动。
进一步的，所述干涉仪镜组3从一侧到另一侧依次包括：反射镜35、折光元件33、1/4波片34、分光棱镜31和偏振分光棱镜32，其中，所述分光棱镜31位于所述偏振分光棱镜32之上。
进一步的，所述参考光经过所述分光棱镜31后分为三束，并通过所述偏振分光棱镜32反射后作为三路干涉信号的参考光；
所述测量光经过所述分光棱镜31后分为三束，其中两束测量光经过所述偏振分光棱镜32反射后，依次通过所述1/4波片34、所述折光元件33后入射至所述测量光栅4，经光栅衍射后返回，再次经过所述偏振分光棱镜32透 射后，与所述三路干涉信号的参考光中的两路干涉，形成两路测量干涉信号；
另一束测量光经过所述偏振分光棱镜32反射后，先通过所述1/4波片34，然后经所述反射镜35反射后沿原光路返回，再次经过所述1/4波片34、经所述偏振分光棱镜32透射后与，所述三路干涉信号的参考光中的另一路干涉，形成一路参考干涉信号。
进一步的，所述干涉仪镜组3中各组件之间紧密邻接固定，集成为一体化结构。
进一步的，所述折光元件33截面为等腰梯形，所述测量光经梯形两侧透射时发生折射，经梯形顶部透射时发生反射。
进一步的，所述其中两束测量光经所述折光元件33后，以特定角度的入射光路至所述测量光栅4，所述特定角度使得衍射光路与所述入射光路重合；所述衍射光路经过所述折光元件33与所述三路干涉信号的参考光中的两路平行干涉，形成两路测量干涉信号。
进一步的，所述干涉测量系统还包括声光调制器2，所述声光调制器2用于对分束后的所述单频激光进行移频。
进一步的，所述干涉测量系统还包括光电转换单元6和电子信号处理部件7，其中：所述光电转换单元6用于接收所述多模光纤5传输的光信号并转换为电信号，以输入至所述电子信号处理部件7；所述电子信号处理部件7接收所述电信号，用以解算所述测量光栅4的线性位移。
与现有技术相比，本发明所提供的二自由度外差光栅干涉测量系统具有以下优点：
(1)本发明的测量系统对比以往的二自由度干涉测量系统，在满足测量精度要求的基础上，可有效的避免了由于干涉仪和测量光栅间存在的转角安装误差和运动过程中存在的角度偏差对测量信号强度的影响。
(2)本发明测量系统的体积小，集成度高，有效地提高了空间利用率和整个应用系统的集成度。
(3)该测量系统能够实现包括两个平动位移的二自由度同时测量，环境敏感度低，测量信号易于处理，分辨率与精度可达纳米甚至更高。
附图说明
通过参考以下具体实施方式及权利要求书的内容并且结合附图，本发明的其它目的及结果将更加明白且易于理解。在附图中：
图1为本发明所述二自由度外差干涉测量系统示意图；
图2为本发明所述干涉仪镜组的结构示意图；
图3为本发明光栅存在转角误差时的示意图；
图4是图3中A-A向的接收光纤与干涉条纹的对比示意图。
图中，1—单频激光器，2—声光调制器，3—干涉仪镜组，4—测量光栅，5—多模光纤，6—光电转换单元，7—电子信号处理部件；31—分光棱镜，32—偏振分光棱镜，33—折光元件，34—1/4波片，35—反射镜。
具体实施方式
下面将结合附图对本发明的技术方案进行清楚、完整地描述，显然，所描述的实施例是本发明一部分实施例，而不是全部的实施例。基于本发明中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都属于本发明保护的范围。
在本发明的描述中，需要说明的是，术语“中心”、“上”、“下”、“左”、“右”、“竖直”、“水平”、“内”、“外”等指示的方位或位置关系为基于附图所示的方位或位置关系，仅是为了便于描述本发明和简化描述，而不是指示或暗示所指的装置或元件必须具有特定的方位、以特定的方位构造和操作，因此不能理解为对本发明的限制。此外，术语“第一”、“第二”、“第三”仅用于描述目的，而不能理解为指示或暗示相对重要性。
在本发明的描述中，需要说明的是，除非另有明确的规定和限定，术语“安装”、“相连”、“连接”应做广义理解，例如，可以是固定连接，也可以是可拆卸连接，或一体地连接；可以是机械连接，也可以是电连接；可以是直接相连，也可以通过中间媒介间接相连，可以是两个元件内部的连通。对于本领域的普通技术人员而言，可以具体情况理解上述术语在本发明中的具体含义。
图1为本发明所述二自由度外差光栅干涉测量系统示意图，如图1所示，所述具有大转角允差的二自由度外差光栅干涉测量系统包括单频激光器1、声光调制器2、干涉仪镜组3、测量光栅4、接收光纤、光电转换单元6和电子 信号处理部件7。优选地，所述接收光纤为多模光纤5，所述测量光栅4为一维反射型光栅。
图2为本发明所述干涉仪镜组的结构示意图，如图2所示，干涉仪镜组3从一侧到另一侧(图2中从左侧到右侧，或从靠近测量光栅4的一侧到另一侧)依次包括：反射镜35、折光元件33、1/4波片34、分光棱镜31和偏振分光棱镜32，其中，所述分光棱镜31位于所述偏振分光棱镜32之上，也就是说，分光棱镜31位于干涉仪镜组上层，偏振分光棱镜32位于干涉仪镜组下层，折光元件33位于干涉仪镜组一侧顶端附近(图2中左侧顶端附近)，为实现高度一体化集成，优选地将干涉仪镜组3中各组件之间紧密邻接固定，集成为一体化结构，更为优选地，各组件之间均采用粘接的方式固定。
图3是本发明光栅存在转角误差时的示意图，如图3所示，当测量光栅相对于理想测量位置存在转角误差时，测量光会偏离参考光，存在一定的夹角，探测器上参考光和测量光两个光斑会偏离，并形成干涉条纹，利用多模光纤5直接接收干涉光信号的局部，并且从图4中可以看出多模光纤5的芯径小于干涉条纹的宽度。
结合图1和图2详细说明光栅干涉测量系统的原理，具体地：
单频激光器1出射单频光，经光纤耦合、光线分束器分束后入射至声光调制器2移频，并经格林透镜准直后得到两路带有频差的偏振光s光，其中一路作为参考光，一路作为测量光。
参考光经过上层分光棱镜31两次分光后得到三束激光，向下入射经过偏振分光棱镜反射后作为三路干涉信号的参考光。
测量光经过分光棱镜31分光后同样得到三束激光向下入射，其中两路经过偏振分光棱镜32反射后，依次通过1/4波片34，折光元件33偏转后入射至测量光栅4，经光栅衍射后，±1级衍射光中包含光栅的转角和位移信息，沿原光路返回，再次经过1/4波片34，偏振分光棱镜32透射后与参考光干涉，形成两路测量干涉信号；另一路测量光经过偏振分光棱镜32反射，依次通过1/4波片34，反射镜35反射后沿原光路返回，再次经过1/4波片34，偏振分光棱镜32透射后与参考光干涉，形成参考干涉信号。
优选地，本发明光路采用利特罗式布置，即所述测量光经折光元件33后偏转后，测量光以特定角度入射至测量光栅4，使得衍射光路与入射光路重合， 衍射光路经过折光元件33形成与参考光平行的测量光，再次通过1/4波片34，偏振分光棱镜32透射后与参考光干涉，形成两路测量信号。
所述两路测量干涉信号和一路参考干涉信号，分别经三个多模光纤5直接耦合干涉光斑的部分区域，共形成三路信号，其信号强度可满足测量需求。传输至光电转换单元6转换为电信号，并输入至电子信号处理部件7进行处理，利用得到的相位信息，解算二自由度线性运动。所述测量光栅4相对于干涉仪镜组3做水平向和垂向两个自由度的线性运动时，电子信号处理部件7将输出二自由度线性位移。
二自由度运动解算的表达式为
Figure PCTCN2019092922-appb-000001
Figure PCTCN2019092922-appb-000002
式中，x,z为光栅位移，φ 1和φ 2为两路测量干涉信号相对于参考干涉信号的相位变化，p为光栅的栅距，λ为激光波长，θ为利特罗角。
上述实施方式中给出的测量系统及结构方案能够实现两个线性自由度的同时测量，且系统测量光路短，受环境影响很小，测量系统采用多模光纤可有效的减少系统部件体积和数量，提高系统的抗干扰能力和系统集成性，可有效的避免由于干涉仪和测量光栅间存在的转角安装误差和运动过程中存在的角度偏差对测量信号强度的影响，测量信号易于处理，线性位移的测量分辨率可达nm级；同时该光栅干涉仪测量系统还具有结构简单，体积小，质量轻，易于安装和布置，应用方便等优点。该二自由度外差光栅干涉仪位移测量系统还可应用于精密机床、三坐标测量机、半导体检测设备等的工件台位移的精密测量中。
尽管前面公开的内容示出了本发明的示例性实施例，但是应当注意，在不背离权利要求限定的范围的前提下，可以进行多种改变和修改。此外，尽管本发明的元素可以以个体形式描述或要求，但是也可以设想具有多个元素，除非明确限制为单个元素。

Claims (11)

  1. 一种二自由度外差光栅干涉测量系统，包括：单频激光器(1)，用于发出单频激光，所述单频激光分束为一束参考光和一束测量光；干涉仪镜组(3)和测量光栅(4)，用于将所述参考光和测量光形成参考干涉信号和测量干涉信号，其特征在于，还包括接收光纤，用于接收所述参考干涉信号和测量干涉信号，所述接收光纤的芯径小于所述参考干涉信号和测量干涉信号的干涉条纹宽度，使得所述接收光纤接收所述参考干涉信号和测量干涉信号的局部。
  2. 根据权利要求1所述的光栅干涉测量系统，其特征在于，所述接收光纤为多模光纤(5)，所述参考干涉信号为一路，所述测量干涉信号为两路；所述两路测量干涉信号和一路参考干涉信号，分别经所述多模光纤(5)耦合接收并输出三路光信号。
  3. 根据权利要求2所述的光栅干涉测量系统，其特征在于，所述干涉测量系统还包括光电转换单元(6)和电子信号处理部件(7)，其中：
    所述光电转换单元(6)用于接收所述多模光纤(5)传输的光信号并转换为电信号，以输入至所述电子信号处理部件(7)；
    所述电子信号处理部件(7)接收所述电信号，用以解算所述测量光栅(4)的线性位移。
  4. 根据权利要求1所述的光栅干涉测量系统，其特征在于，所述测量光栅(4)相对于所述干涉仪镜组(3)做水平向和垂向两个自由度的线性运动。
  5. 根据权利要求2所述的光栅干涉测量系统，其特征在于，所述测量光栅(4)相对于所述干涉仪镜组(3)做水平向和垂向两个自由度的线性运动。
  6. 根据权利要求1所述的光栅干涉测量系统，其特征在于，所述干涉仪镜组(3)从一侧到另一侧依次包括：反射镜(35)、折光元件(33)、1/4波片(34)、分光棱镜(31)和偏振分光棱镜(32)，其中，所述分光棱镜(31)位于所述偏振分光棱镜(32)之上。
  7. 根据权利要求6所述的光栅干涉测量系统，其特征在于，所述参考光经过所述分光棱镜(31)后分为三束，并通过所述偏振分光棱镜(32)反射后作为三路干涉信号的参考光；
    所述测量光经过所述分光棱镜(31)后分为三束，其中两束测量光经过所述偏振分光棱镜(32)反射后，依次通过所述1/4波片(34)、所述折光元件(33)后入射至所述测量光栅(4)，经光栅衍射后返回，再次经过所述偏振分光棱镜(32)透射后，与所述三路干涉信号的参考光中的两路干涉，形成两路测量干涉信号；
    另一束测量光经过所述偏振分光棱镜(32)反射后，先通过所述1/4波片(34)，然后经所述反射镜(35)反射后沿原光路返回，再次经过所述1/4波片(34)、经所述偏振分光棱镜(32)透射后与所述三路干涉信号的参考光中的另一路干涉，形成一路参考干涉信号。
  8. 根据权利要求7所述的光栅干涉测量系统，其特征在于，所述其中两束测量光经所述折光元件(33)后，以特定角度的入射光路至所述测量光栅(4)，所述特定角度使得衍射光路与所述入射光路重合；所述衍射光路经过所述折光元件(33)与所述三路干涉信号的参考光中的两路平行干涉，形成两路测量干涉信号。
  9. 根据权利要求6所述的光栅干涉测量系统，其特征在于，所述干涉仪镜组(3)中各组件之间邻接固定，集成为一体化结构。
  10. 根据权利要求6所述的光栅干涉测量系统，其特征在于，所述折光元件(33)截面为等腰梯形，所述测量光经梯形两侧透射时发生折射，经梯形顶部透射时发生反射。
  11. 根据权利要求1所述的光栅干涉测量系统，其中，所述干涉测量系统还包括声光调制器(2)，用于对分束后的单频激光进行移频。
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