CN105823422B - A kind of two degrees of freedom heterodyne grating interferometer displacement measurement system and method - Google Patents

Abstract

A two-degree-of-freedom heterodyne grating interferometer displacement measurement system and method, which includes a dual-frequency laser, a grating interferometer, a measurement grating, a receiver, and a signal processing unit; the grating interferometer includes a lateral displacement beamsplitter prism, a polarization beamsplitter prism, 1/4 wave plate, mirror and fiber coupler; the method realizes displacement measurement based on grating diffraction, optical Doppler effect and optical-beat frequency principle. The laser of the dual-frequency laser is incident on the interferometer, and the optical signal is output to the signal processing unit after measuring the grating. When the interferometer and the measuring grating make a two-degree-of-freedom linear relative motion, the system can output two linear displacements; the measurement system adopts Littrow Incidence conditions, the measurement target has a large passive motion tolerance, and can measure two linear displacements at the same time, and the accuracy can reach nanometer level or even higher; it has short optical path, small size, compact structure, light weight, and low requirements for measurement gratings And other advantages, suitable for two-degree-of-freedom high-precision long-stroke displacement measurement.

Description

A displacement measurement system and method of a two-degree-of-freedom heterodyne grating interferometer

technical field

The invention relates to a measurement system and method of a two-degree-of-freedom heterodyne grating interferometer, in particular to the displacement measurement of an ultra-precision workpiece table, and belongs to the technical field of displacement measurement.

Background technique

As a typical displacement sensor, the grating measurement system is widely used in many electromechanical equipment. The measurement principle of the grating measurement system is mainly based on the Moiré fringe principle and the diffraction interference principle. As a well-developed displacement sensor, the grating measurement system based on the Moiré fringe principle has become the first choice for displacement measurement of many electromechanical equipment due to its long measuring range, low cost, and easy installation and adjustment, but the accuracy is usually on the order of microns, which is common for general industrial applications.

Ultra-precision displacement measurement technology has important applications in industrial metrology equipment such as three-coordinate measuring machines, ultra-precision workpiece tables, and meter-level grating manufacturing equipment. Displacement Measuring Interferometry (DMI) based on laser wavelength is one of the most precise displacement measurement techniques in industrial metrology. Ultra-precision workpiece table has become the most representative type of system in ultra-precision displacement measurement technology due to its high-speed, high-acceleration, large-stroke, ultra-precision, multi-degree-of-freedom and other motion characteristics. In order to realize the above-mentioned movement, the ultra-precision workpiece table usually uses a dual-frequency laser interferometer measurement system to measure the multi-degree-of-freedom displacement of the ultra-precision workpiece table. However, with the continuous improvement of motion indicators such as measurement accuracy, measurement distance, and measurement speed, the dual-frequency laser interferometer has a series of problems such as environmental sensitivity, difficulty in improving measurement speed, space occupation, high price, and difficulty in designing, manufacturing and controlling the target workpiece table. The problem is difficult to meet the measurement needs.

In response to the above problems, major companies and research institutions in the field of ultra-precision measurement in the world have carried out a series of research, the research mainly focuses on the grating measurement system based on the principle of diffraction interference, and the research results have been disclosed in many patent papers. Netherlands ASML company US patent US7,102,729 B2 (disclosure date August 4, 2005), US7,483,120 B2 (disclosure date November 15, 2007), US7,940,392 B2 (disclosure date December 24, 2009) , Publication No. US2010/0321665 A1 (published on December 23, 2010) discloses a planar grating measurement system and layout scheme applied to ultra-precision workpiece tables of lithography machines. The measurement system mainly uses one-dimensional or two-dimensional The planar grating cooperates with the reading head to measure the horizontal large-stroke displacement of the workpiece table, and height sensors such as eddy currents or interferometers are used to measure the displacement in the height direction, but the application of various sensors limits the measurement accuracy of the workpiece table. U.S. Patent Publication No. US2011/0255096 A1 (published on October 20, 2011) of ZYGO Corporation of the United States discloses a grating measurement system applied to an ultra-precision workpiece table of a lithography machine. The measurement system also uses a two-dimensional grating with a specific The reading head realizes displacement measurement, which can measure horizontal and vertical displacement simultaneously, but the structure is complicated, and the cost of two-dimensional grating is extremely expensive; Japanese CANON Corporation US Patent Publication No. US2011/0096334 A1 (publication date April 28, 2011) A heterodyne interferometer is disclosed, in which a grating is used as an objective mirror, but the interferometer can only realize one-dimensional measurement. In the research paper "Design and construction of a two-degree-of-freedom linear encoder for nanometric measurement of stage position and straightness. Precision Engineering 34 (2010) 145-155", Japanese scholar GAOWEI proposed a single encoder using the principle of diffraction interference. Frequency two-dimensional grating measurement system, which can realize horizontal and vertical displacement measurement at the same time, but due to the use of single-frequency laser, the measurement signal is susceptible to interference, and the accuracy is difficult to guarantee. In addition, Chinese Patent Literature Publication Nos. CN103759657A (publication date: April 30, 2014) and CN103759656A (publication date: April 30, 2014) respectively disclose a heterodyne grating interferometer measurement system. The structure of the reading head makes its travel very small when measuring the vertical direction, and it cannot measure a larger stroke for the vertical movement, so the application range is limited.

Contents of the invention

Considering the limitations of the above-mentioned technical solutions, the object of the present invention is to provide a displacement measurement system and method of a two-degree-of-freedom heterodyne grating interferometer, which can utilize the grating Littrow principle to realize an optical four-division structure in the horizontal direction and realize sub- Measurement of nanometer or even higher resolution and precision; realize optical subdivision structure in the vertical direction, and realize measurement of nanometer or higher resolution and precision; at the same time, the grating interferometer measurement system should also have a simple structure, small size, and high quality. Lightweight, easy to install, convenient to apply and so on. Using this measurement system as an ultra-precision workpiece table displacement measurement device can effectively reduce the shortcomings of the laser interferometer measurement system in the application of ultra-precision workpiece tables, and improve the performance of ultra-precision workpiece tables for lithography machines. The two-degree-of-freedom heterodyne grating interferometer displacement measurement system can also be applied to precision measurement of multi-degree-of-freedom displacement of workpiece tables such as precision machine tools, three-coordinate measuring machines, and semiconductor testing equipment, and it has a simple structure, small size, and high quality. Lightweight, easy to install, convenient to apply and so on.

Technical scheme of the present invention is as follows:

A two-degree-of-freedom heterodyne grating interferometer displacement measurement system includes a dual-frequency laser, a grating interferometer, a measuring grating, a receiver, and a signal processing unit; it is characterized in that the grating interferometer includes a base with a mounting groove, a lateral Shift beamsplitter, first polarization beamsplitter, second polarization beamsplitter, reference grating, first 1/4 wave plate, second 1/4 wave plate, third 1/4 wave plate, fourth 1/4 wave plate , the first reflector, the second reflector, the third reflector, the first fiber coupler and the second fiber coupler;

The dual-frequency laser 1 emits the dual-frequency laser to the lateral displacement beam splitter 6 to form the first transmitted light and the first reflected light, wherein the first transmitted light enters the first polarization beam splitter 7, and the first reflected light enters the second polarization beam splitter Prism 8; the first transmitted light generates the second transmitted light and the second reflected light after passing through the first polarizing beam splitter prism 7; wherein the second transmitted light passes through the first 1/4 wave plate 10 and the first reflector 14 successively, Taking the Littrow included angle corresponding to the measuring grating 3 as the incident angle, it hits the measuring grating 3 and diffracts, and the formed minus-order diffracted light returns along the original path, and passes through the first reflector 14 and the first 1/4 wave again. The plate 10 is incident to the first polarizing beam splitter prism 7 and reflected to form the first measuring light; the second reflected light passes through the second 1/4 wave plate 11 and the second reflecting mirror 15 in order to correspond to the light intensity of the measuring grating 3 The included angle is the incident angle and hits the measuring grating 3 and diffracts, the formed positive first-order diffracted light returns along the original path, and enters the first polarized light through the second reflector 15 and the second 1/4 wave plate 1) again The beam-splitting prism 7 is transmitted to form the second measurement light; the first reflected light generates the third transmitted light and the third reflected light after passing through the second polarizing beam-splitting prism 8; wherein the third transmitted light passes through the fourth 1/4 wave in sequence After the sheet 13 and the third reflecting mirror 16, it hits the measuring grating 3 with the Littrow included angle corresponding to the measuring grating 3 as the incident angle and diffracts, and the formed positive first-order diffracted light returns along the original path and passes through the third reflector again. The reflector 16 and the fourth 1/4 wave plate 13 are incident to the second polarization beam splitter prism 8 and reflected to form the third measurement light; the third reflected light passes through the third 1/4 wave plate 12 in sequence to correspond to the reference grating The Littrow included angle of 9 is the incident angle and hits the reference grating 9 and diffracts, and the formed positive first-order diffracted light returns along the original path, and enters the second polarization beam splitter prism 8 again through the third 1/4 wave plate 12 and transmission occurs to form the first beam of reference light; the first measurement light and the second measurement light are combined at the first polarization beam splitter prism 7 and then incident to the first optical fiber coupler 17 with a built-in lens and deflection plate to obtain the first combination The optical signal is then connected to the receiver 4 through an optical fiber; the third measurement light and the first reference light are finally combined at the second polarization beam splitter 8 and then incident to the second optical fiber coupler 18 with a built-in lens and deflection plate to obtain The second combined light signal is then connected to the receiver 4 through an optical fiber, and the two combined light signals are converted into electrical signals in the receiver 4, and then input to the signal processing unit 5 for processing; when the measuring grating 3 fixed on the moving platform is relatively When the grating interferometer 2 performs a linear motion with two degrees of freedom, the signal processing unit 5 will output a linear displacement with two degrees of freedom. In the above technical solution, the measuring grating adopts a one-dimensional reflective grating. The lateral displacement beamsplitter, polarization beamsplitter, reflector and reference grating are all fixed on the base through the corresponding grooves on the installation base, and the 1/4 slide is fixed on the polarization reflector by bonding.

A method for measuring the displacement of a large-stroke two-degree-of-freedom heterodyne grating interferometer using the above-mentioned measuring system includes the following steps:

1) Horizontal displacement measurement:

The light intensity I _1-2 of the first combined light signal formed by the first measurement light and the second measurement light is:

Wherein E ₁ represents the first measurement light vector, E ₂ represents the second measurement light vector, Φ _m represents the phase change of the first combined light signal, _Im represents the DC component of the light intensity of the first combined light signal, Δf ₁ represents the frequency difference between the first measurement light and the second measurement light.

The phase change Φ _m of the first combined light signal is:

Φ _m ＝(Φ ₂ +Δφ ₂ )-(Φ ₁ +Δφ ₁ )

Among them, Φ ₁ and Φ ₂ represent the phase changes of the first measurement light and the second measurement light due to the horizontal movement of the measurement grating 3, and Δφ ₁ and Δφ ₂ represent the first measurement light and the second measurement light due to the vertical movement of the measurement grating 3. A phase change due to directional motion, and:

Δφ ₁ = Δφ ₂

In the formula, N is the electronic subdivision multiple of the signal processing unit 5, _km is the count of the signal processing unit 5 to the phase change of the first combined light signal, and Δx represents the displacement of the measurement grating 3 in the horizontal direction;

Measure the displacement Δx of the grating 3 in the horizontal direction as:

Where x _res represents the horizontal measurement distance corresponding to the unit phase count of the signal processing unit 5;

2) Vertical displacement measurement:

a. The light intensity I _3-4 of the second combined light signal formed by the third measurement light and the first reference light is:

Where E ₃ represents the third measurement light vector, E ₄ represents the first reference light vector, Φ _n represents the phase change of the second combined light signal, _In represents the DC component of the light intensity of the first combined light signal, Δf ₂ represents the frequency difference between the first measurement light and the second measurement light.

The phase change Φ _n of the second combined optical signal is:

Φ _n ＝Φ ₃ +ΔΦ ₃

Among them, Φ ₃ represents the phase change of the third measurement light due to the horizontal movement of the measurement grating 3, and Δφ ₃ represents the phase change of the third measurement light due to the vertical movement of the measurement grating 3, and: Φ ₃ = Φ ₂ ;

The third measurement light phase change Δφ ₃ is expressed as:

Among them, Φ _r represents the vertical motion component of the measurement grating, which makes the light spot on the measurement grating 3 scan a section of grid line and the phase change of the second combined light signal caused by the grating Doppler effect, and Φ _l represents the vertical motion component of the measurement grating 3 The phase change of the second composite light signal is caused by the laser Doppler effect when the diffraction point moves relative to the incident direction;

b. Measure the displacement X of the light spot on the grating line caused by the vertical motion component of the grating 3:

X＝x ₀ ×Φ _r

The displacement L of the grating diffraction point along the incident direction caused by measuring the vertical motion component of the grating 3 is:

L＝l ₀ ×Φ _l

and:

Among them, θ represents the angle between the displacement X and the displacement L, α represents the Littrow angle corresponding to the measurement grating, x ₀ represents the grating displacement corresponding to the unit phase count, l ₀ represents the incident direction displacement corresponding to the unit phase count, and p represents Measuring the grating constant of the grating, N represents the electronic subdivision multiple of the signal processing unit, λ is the output laser wavelength of the dual-frequency laser, and N is the electronic subdivision multiple of the signal processing unit 5;

c. The relationship between Φ _l and Φ _r is expressed as:

From this we get:

The vertical displacement Δy can be deduced from the obtained Φ _l :

Where N is the electronic subdivision multiple of the signal processing unit, k _n is the phase count of the second combined light signal by the signal processing unit, and y _res represents the vertical movement distance corresponding to the unit operation result of the phase count of the two combined light signals.

A two-degree-of-freedom heterodyne grating interferometer displacement measurement system and method provided by the present invention has the following advantages and outstanding effects:

The measurement system uses the grating Littrow principle to realize the optical four-division structure in the horizontal direction to achieve sub-nanometer or even higher resolution and precision measurement; realize the optical two-division structure in the vertical direction to achieve nanometer or even higher resolution and precision measurement; the measurement system can realize the simultaneous measurement of two linear degrees of freedom and large stroke displacement; the system can realize the simultaneous measurement of two linear degrees of freedom displacement only through a one-dimensional linear grating, which greatly reduces the production cost; at the same time, the The grating interferometer measurement system also has the advantages of simple structure, small size, light weight, easy installation, and convenient application. It is applied to the displacement measurement of the ultra-precision workpiece table of the lithography machine. Compared with the laser interferometer measurement system, on the basis of meeting the measurement requirements, it can effectively reduce the volume and quality of the workpiece table, greatly improve the dynamic performance of the workpiece table, and make the workpiece table as a whole Comprehensive performance improvement. The two-degree-of-freedom heterodyne grating interferometer displacement measurement system can also be applied to the precise measurement of multi-degree-of-freedom displacement of workpiece tables such as precision machine tools, three-coordinate measuring machines, and semiconductor testing equipment.

Description of drawings

Fig. 1 is a schematic diagram of a displacement measurement system of a heterodyne grating interferometer according to the present invention.

Fig. 2 is a schematic diagram of the internal structure of the embodiment of the grating interferometer of the present invention.

Fig. 3 is a schematic diagram of the measurement principle of the method of the present invention.

In the figure, 1—dual-frequency laser, 2—grating interferometer, 3—measurement grating, 4—receiver, 5—signal processing unit; 6—lateral displacement beam splitter, 7—first polarization beam splitter, 8—second Two polarization beam splitters, 9—reference grating, 10—the first 1/4 wave plate, 11—the second 1/4 wave plate, 12—the third 1/4 wave plate, 13—the fourth 1/4 wave plate, 14—first reflector, 15—second reflector, 16—third reflector, 17—first fiber coupler, 18—second fiber coupler, 19—installation base.

Detailed ways

The structure, principle and specific implementation of the present invention will be further described in detail below in conjunction with the accompanying drawings.

Referring to Fig. 1 and Fig. 2, the two-degree-of-freedom heterodyne grating interferometer displacement measurement system provided by the present invention includes a dual-frequency laser 1, a grating interferometer 2, a measuring grating 3, a receiver 4 and a signal processing unit 5; the grating interferometer The instrument includes a base with a mounting groove, a lateral displacement beamsplitter prism 6, a first polarization beamsplitter prism 7, a second polarization beamsplitter prism 8, a reference grating 9, a first 1/4 wave plate 10, a second 1/4 wave plate plate 11, the third 1/4 wave plate 12, the fourth 1/4 wave plate 13, the first reflector 14, the second reflector 15, the third reflector 16, the first fiber coupler 17 and the second fiber coupler Device 18.

After the dual-frequency laser 1 emits the dual-frequency laser to the lateral displacement beam splitter 6, the transmitted light enters the first polarization beam splitter 7, and the reflected light enters the second polarization beam splitter 8; the light incident on the first polarization beam splitter 7 passes through the second polarization beam splitter After a polarizing beam splitter 7 produces transmitted light and reflected light; where the transmitted light passes through the first 1/4 wave plate 10 and the first reflecting mirror 14 in sequence, and takes the Littrow included angle corresponding to the measuring grating 3 as the incident angle Diffraction occurs on the measurement grating 3, and the negative first-order diffracted light returns along the original path, and enters the first polarization beam splitter prism 7 through the first reflector 14 and the first 1/4 wave plate 10 again and is reflected to form the second 1. Measuring light: After the reflected light passes through the fourth 1/4 wave plate 13 and the second mirror 15 in sequence, it hits the measuring grating 3 at the incident angle corresponding to the Littrow angle of the measuring grating 3 and diffracts to form The positive first-order diffracted light returns along the original path, passes through the second reflector 15 and the fourth 1/4 wave plate 13 again, enters the first polarization beam splitter prism 7 and transmits it to form the second measurement light; it enters the second polarization beam splitter The light from the prism 8 generates transmitted light and reflected light after passing through the second polarizing beam splitter prism 8; where the transmitted light passes through the third 1/4 wave plate 12 and the third reflecting mirror 16 in order to correspond to the Littrow of the measuring grating 3 The included angle is the incident angle and hits the measuring grating 3 and diffracts, and the formed positive first-order diffracted light returns along the original path, and enters the second polarization beam splitter prism through the third reflector 16 and the third 1/4 wave plate 12 again 8 and reflected to form the third measurement light; after the reflected light passes through the second 1/4 wave plate 11 in sequence, it hits the reference grating 9 at the Littrow angle corresponding to the reference grating 9 as the incident angle and diffracts to form The positive first-order diffracted light returns along the original path, and enters the second polarization beam splitter prism 8 through the fourth half-wave plate 12 again and is transmitted to form the first beam of reference light; the first measurement light and the second measurement light After the light is combined at the first polarization beam splitter 7, it enters the fiber coupler 17 with the built-in lens and deflection plate to obtain the first combined light signal, and then enters the receiver 4 through the optical fiber; the third measurement light and the first reference light Finally, the light is combined at the second polarization beam splitter prism 8 and then incident to the fiber coupler 17 with built-in lens and deflection plate to obtain the second combined light signal, which is then connected to the receiver 4 through the optical fiber, and the two combined light signals are transmitted to the receiver 4 It is converted into an electrical signal, and then input to the signal processing unit 5 for processing; when the measuring grating 3 fixed on the moving platform makes a two-degree-of-freedom linear motion relative to the grating interferometer 2, the signal processing unit 5 will output a two-degree-of-freedom linear displacement.

Specific measurement method:

1) Horizontal displacement measurement:

The dual-frequency orthogonally polarized laser light emitted by the dual-frequency laser (p-polarized light with a frequency of _f1 , and s-polarized light with a frequency of _f2 ) enters the first polarization beam-splitter prism 7 through the lateral displacement beam-splitting prism 6, and the dual-frequency After the orthogonally polarized laser passes through the first polarizing beam splitter 7, the p-polarized light of frequency f ₁ is transmitted, and the s-polarized light of frequency f ₂ is reflected; the p-polarized light of frequency f ₁ is transmitted through the 1/ After the 4-wave plate becomes left-handed polarized light, the left-handed polarized light enters the measurement grating 3 under the Littrow condition after passing through the mirror and diffracts, and the -1 order diffracted light returns along the original optical path, and becomes It is s-polarized light, which is reflected after reaching the PBS; the s-polarized light with frequency f ₂ is reflected and becomes left-handed polarized light after passing through the 1/4 wave plate arranged with the fast axis at 45°. Raw conditions are incident on the measuring grating 3 and diffracted, and the +1 order diffracted light returns along the original optical path, and becomes p-polarized light after passing through the 1/4 wave plate again, and then transmits after reaching the PBS; the two paths of measuring light are coincident and incident on the optical fiber coupling The laser (built-in lens and polarizer) forms an optical beat frequency signal and transmits it to the electronic phase meter through the optical fiber, and the dual-frequency laser outputs the reference signal to the electronic phase meter at the same time; the electronic phase meter uses the reference signal and the measurement signal to read the grating movement in the measurement signal displacement information.

According to the grating Doppler effect, when the measuring grating moves Δx along the direction of the grating vector, the phase change of ±1-level measuring light is:

In the formula, p represents the grating constant of the measurement grating 3, Φ ₊₁ represents the phase change of the +1 order diffracted light, and Φ _-1 represents the phase change of the -1 order diffracted light.

The light vector of the dual-frequency laser emitted by the laser is:

E ₀ is the electric field vector amplitude of the dual-frequency laser, and is the initial phase offset. _f1 is the frequency of one of the beams and _f2 is the frequency of the other beam.

The optical path of the first measurement light is: BS(T)→PBS1(T)→QW1(45)→M1(R)→G3(D)→M1(R)→QW1(45)→PBS1(R)→L→ P(45), then the optical vector of the negative level measuring light after optical fiber coupling is:

E ₁ ＝J _P J _PBR J _QW(45) J _M J _G J _M J _QW(45) J _PBT J _BS(T) E ₀ (3)

Among them, BS(T) means that the light is transmitted through the lateral displacement beam-splitting prism, PBS1(T) means that the light is transmitted through the first polarization beam-splitting prism, PBS1(R) means that the light is reflected by the first polarization beam-splitting prism, and QW1(45) means that the light passes through The first 1/4 glass slide arranged at 45 degrees to the fast axis, M1(R) indicates that the light is reflected on the first mirror, G3(D) indicates that the light is diffracted on the measurement grating, L indicates the built-in fiber coupler Lens, P(45) indicates the built-in analyzer coupled with the fiber and arranged at 45 degrees.

The optical path of the second measuring light is: BS(T)→PBS1(R)→QW2(45)→M2(R)→G3(D)→M2(R)→QW2(45)→PBS1(T)→L→ P(45), then the optical vector of the negative level measuring light after optical fiber coupling is:

E ₂ ＝J _P J _PBT J _QW(45) J _M J _G J _M J _QW(45) J _PBR J _BS(T) E ₀ (4)

Among them, PBS1(R) indicates that the light is reflected by the first polarizing beam splitter, QW2(45) indicates that the light passes through the second 1/4 glass slide arranged at 45 degrees to the fast axis, and M2(R) indicates that the light is reflected on the first mirror .

Therefore the light intensity I _1-2 of the first measurement light and the second measurement photosynthetic light is:

Wherein E ₁ represents the first measurement light vector, E ₂ represents the second measurement light vector, Φ _m represents the phase change of the first combined light signal, _Im represents the DC component of the light intensity of the first combined light signal, Δf ₁ represents the frequency difference between the first measurement light and the second measurement light.

The phase change Φ _m of the first combined light signal is:

Φ _m ＝(Φ ₂ +Δφ ₂ )-(Φ ₁ +Δφ ₁ ) (6)

Among them, Δφ ₁ and Δφ ₂ represent the phase changes of the first measurement light and the second measurement light due to the vertical movement of the measurement grating 3, and Φ ₁ and Φ ₂ represent the first measurement light and the second measurement light due to the horizontal movement of the measurement grating 3. The phase change produced by directional movement, N is the electronic subdivision multiple of the signal processing unit 5, _km is the phase count of the first combined light signal by the signal processing unit 5, and the first measurement light is -1 order diffracted light, the second The second measurement light is +1 order diffracted light, therefore:

Φ ₂ +Δφ ₂ =Φ ₊₁ , Φ ₁ +Δφ ₁ =Φ ₋₁ . (7)

Since the angles of the first measurement light and the second side measurement light are symmetrical with respect to the vertical line of the measurement grating surface and -1 order and +1 order diffracted light are used respectively, therefore:

Δφ ₁ = Δφ ₂ (8)

Then the phase change Φ _m of the first combined optical signal is:

And because of the phase change Φ _m can be expressed as:

Therefore, (9) and (10) measure the displacement in the horizontal direction of the grating 3 as:

Where x _res represents the horizontal measurement distance corresponding to the count of the unit signal processing unit, _km is the count of the phase change of the first composite light signal by the signal processing unit 5, and Δx represents the displacement of the measuring grating 3 in the horizontal direction.

2) Vertical displacement measurement:

The dual-frequency orthogonally polarized laser light emitted by the dual-frequency laser (the frequency is the p-polarized light of _f1 , and the frequency is the s-polarized light of _f2 ), is incident on the second polarization beam-splitting prism 8 after being reflected by the lateral displacement beam-splitting prism 6, After the dual-frequency orthogonally polarized laser passes through the first polarization beam splitter 8, the p-polarized light of frequency f ₁ is transmitted, and the s-polarized light of frequency f ₂ is reflected; the p-polarized light of frequency f ₁ is transmitted and arranged at 45° through the fast axis After the 1/4 wave plate becomes left-handed polarized light, the left-handed polarized light is incident on the measurement grating (3) under the Littrow condition after passing through the reflector and diffracted, and the +1 order diffracted light returns along the original optical path and passes through 1/4 again After the wave plate becomes s-polarized light, it is reflected after reaching the PBS; the s-polarized light with frequency f ₂ is reflected and then becomes left-handed polarized light after passing through the 1/4 wave plate with the fast axis arranged at 45°, and is determined by the Littrow condition Incident to the reference grating and diffracted, the +1 order diffracted light returns along the original optical path, becomes p-polarized light after passing through the 1/4 wave plate again, and transmits after reaching the PBS; lens and polarizer) to form an optical beat frequency signal and transmit it to the electronic phase meter through an optical fiber, and the dual-frequency laser simultaneously outputs a reference signal to the electronic phase meter. The electronic phase meter uses the reference signal and the measurement signal to read out the grating movement displacement information in the measurement signal.

The optical path of the third measurement light is: BS(R)→PBS2(T)→QW4(45)→M3(R)→G3(D)→M3(R)→QW4(45)→PBS2(R)→L→ P(45), then the optical vector of the negative level measuring light after optical fiber coupling is:

E ₃ ＝J _P J _PBR J _QW(45) J _M J _G J _M J _QW(45) J _PBT J _BSR E ₀ (12)

Among them, BS(R) means that the light is reflected by the lateral displacement beam splitting prism, PBS2(T) means that the light is transmitted through the second polarizing beam splitting prism, PBS2(R) means that the light is reflected by the second polarizing beam splitting prism, QW4(45) means that the light passes through The fourth 1/4 glass slide, M3(R) arranged at 45 degrees to the fast axis indicates that light is reflected on the third reflector.

The optical path of the first reference light is: BS(R)→PBS2(R)→QW3(45)→G9(D)→QW3(45)→PBS2(T)→L→P(45), after optical fiber coupling The light vector of the negative first-order measurement light of is:

E ₄ ＝J _P J _PBT J _QW(45) J _G J _QW(45) J _PBR J _BSR E ₀ (13)

Among them, QW3 (45) means that the light passes through the third 1/4 slide arranged at 45 degrees to the fast axis, and G9 (D) means that the light is diffracted on the reference grating.

Therefore, the intensity of the third measurement light and the first reference photosynthetic light is:

Wherein E ₃ represents the first measurement light vector, E ₄ represents the second measurement light vector, Φ _n represents the phase change of the second combined light signal, _Im represents the direct current component of the light intensity of the first combined light signal, Δf ₁ represents the frequency difference between the first measurement light and the second measurement light.

The phase change of the second combined optical signal is:

Φ _n ＝Φ ₃ +ΔΦ ₃ (15)

Among them, Φ ₃ represents the phase change of the third measurement light due to the movement of the measurement grating 3 in the horizontal direction, Δφ ₃ represents the phase change of the third measurement light due to the movement of the measurement grating 3 in the vertical direction, and due to the second measurement light, the third measurement light Both are the +1 order diffracted light on the measurement grating and are parallel to each other, so the phase changes of the second measurement light and the third measurement light caused by the grating Doppler effect of the horizontal motion component of the measurement grating 3 are the same, that is

Φ ₂ = Φ ₃ (16)

There are (6), (8) formula Δφ ₃ can be expressed as:

Among them, Φ _r represents the vertical motion component of the measurement grating that makes the light spot on the measurement grating 3 sweep a section of grating line and the phase change of the second combined light signal due to the grating Doppler effect, and Φ _l represents the vertical motion component of the measurement grating 3 The phase change of the second composite light signal is caused by the laser Doppler effect when the diffraction point moves relative to the incident direction.

Let the vertical motion component cause the displacement of the light along the incident direction to be L, and the displacement of the light spot on the grating line to be X, as shown in Figure 3, the wavelength of the laser emitted by the laser 1 is λ, the grating constant of the measuring grating 3 is p, and the signal The electronic subdivision multiple of the processing unit 5 is N,

but:

X＝x ₀ ×Φ _r (18)

L＝l ₀ ×Φ _l (19)

where x ₀ represents the grating displacement corresponding to the unit phase count, l ₀ represents the incident direction displacement corresponding to the unit phase count, and:

Because the laser light is incident on the grating under the Littrow condition, the angle θ between the displacement L and the displacement X is equal to the Littrow angle α corresponding to the measurement grating.

so:

From the above formulas (18), (19), (20), (21), (22) can be obtained:

And by formula (16), get:

And because the vertical displacement Δy=Lcosθ

From formula (19), (24):

In the formula, N is the electronic subdivision multiple of the electronic phase meter, _km and k _n are the phase counts of the first combined light signal and the second combined light signal by the electronic phase meter respectively, and y _res represents the unit of the phase count of the two combined light signals The vertical movement distance corresponding to the operation result.

Claims (5)

1. a kind of big stroke two degrees of freedom heterodyne grating interferometer displacement measurement system, the system include two-frequency laser (1), light Grating interferometer (2) measures grating (3), receiver (4) and signal processing unit (5)；It is characterized in that：Grating interferometer (2) wraps It includes with reeded mounting seat (19), lateral displacement Amici prism (6), the first polarization splitting prism (7), the second polarization spectro Prism (8), reference grating (9), the first quarter wave plate (10), the second quarter wave plate (11), third quarter wave plate (12), the 4th 1/4 wave Piece (13), the first speculum (14), the second speculum (15), third speculum (16), the first fiber coupler (17) and second Fiber coupler (18)；After two-frequency laser (1) is emitted double-frequency laser to lateral displacement Amici prism (6), the first transmission is formed Light and the first reflected light, wherein the first transmitted light enters the first polarization splitting prism (7), the first reflected light enters the second polarization point Light prism (8)；First transmitted light is generating the second transmitted light and the second reflected light after the first polarization splitting prism (7)；Its In the second transmitted light successively after the first quarter wave plate (10), the first speculum (14), with the corresponding Li Te for measuring grating (3) Sieve angle is that incidence angle beats on measuring grating (3) and diffraction occurs, and the negative one order diffraction light of formation passes through again along backtracking It crosses the first speculum (14) and the first quarter wave plate (10) is incident to the first polarization splitting prism (7) and reflects, form first Measure light；After the second quarter wave plate (11), the second speculum (15), grating (3) is measured to correspond to successively for second reflected light Littrow angle is that incidence angle beats on measuring grating (3) and diffraction occurs, the positive first-order diffraction light of formation along backtracking, then It is secondary to be incident to the first polarization splitting prism (7) by the second speculum (15) and the second quarter wave plate (11) and transmit, it is formed Second measures light；First reflected light is generating third transmitted light and third reflected light after the second polarization splitting prism (8)；Its After the 4th quarter wave plate (13), third speculum (16), the Li Te of grating (3) is measured with correspondence successively for middle third transmitted light Sieve angle is that incidence angle beats on measuring grating (3) and diffraction occurs, and the positive first-order diffraction light of formation passes through again along backtracking It crosses third speculum (16) and the 4th quarter wave plate (13) is incident to the second polarization splitting prism (8) and reflects, form third Measure light；Third reflected light successively after third quarter wave plate (12), the Littrow angle to correspond to reference grating (9) be into Diffraction is beaten in reference grating (9) and occurred to firing angle, and the positive first-order diffraction light of formation again passes by the 3rd 1/4 along backtracking Wave plate (12) is incident to the second polarization splitting prism (8) and transmits, and forms the first reference light；First, which measures light and second, surveys Amount light is incident to the first fiber coupler of built-in lens and deflection film after realization closing light at the first polarization splitting prism (7) (17) the first closing light signal is obtained, using intelligent acess receiver (4)；Third measures light and the first reference light finally second It is incident to built-in lens after realizing closing light at polarization splitting prism (8) and the second fiber coupler (18) of deflection film obtains second Closing light signal, using intelligent acess receiver (4), two beam closing light signals switch to electric signal in receiver (4), then are input to Signal processing unit (5) is handled；When the measurement grating (3) for being fixed on sports platform does two relative to grating interferometer (2) When the linear movement of degree of freedom, signal processing unit (5) will export two degrees of freedom linear displacement.

2. a kind of big stroke two degrees of freedom heterodyne grating interferometer displacement measurement system according to claim 1, feature It is：Measurement grating is one-dimensional linear grating.

3. a kind of big stroke two degrees of freedom heterodyne grating interferometer displacement measurement system according to claim 1, feature It is：Quarter wave plate fast axle is arranged with polarization of light direction at 45 degree.

4. a kind of big stroke two degrees of freedom heterodyne grating interferometer displacement measurement system according to claim 1, feature It is：Lateral displacement Amici prism (6), the first polarization splitting prism (7), the second polarization splitting prism (8), reference grating (9), First speculum (14) and the second speculum (15) are all in the groove being fixed on by way of bonding in mounting seat (19).

5. using a kind of big stroke two degrees of freedom heterodyne grating interferometer displacement measurement method of system as described in claim 1, It is characterized in that this method comprises the following steps：

1) horizontal direction displacement measurement：

First, which measures light and second, measures the first closing light signal light intensity I of light formation_1-2For：

Wherein E₁Indicate that first measures light light vector, E₂Indicate that second measures light light vector, Φ_mIndicate the phase of the first closing light signal Position variation, I_mIndicate the DC component of the first closing light signal light intensity signal light intensity, Δ f₁Indicate that first measures light and the second measurement light The difference of frequency；

The phase change Φ of first closing light signal_mFor：

Φ_m=(Φ₂+Δφ₂)-(Φ₁+Δφ₁)

Wherein Φ₁And Φ₂Indicate that first measures light and the second measurement light due to measuring the generation of grating (3) horizontal motion respectively Phase change, Δ φ₁With Δ φ₂Indicate that first measures light and the second measurement light due to measuring grating (3) vertical direction fortune respectively The phase change of movable property life, and：

Δφ₁=Δ φ₂

N is the electronic fine-grained multiple of signal processing unit (5), k in formula_mIt is signal processing unit (5) to the first closing light signal phase The counting of variation, Δ x indicate to measure the displacement of grating (3) in the horizontal direction；

Measuring grating (3), displacement x is in the horizontal direction：

Wherein x_resIndicate that the unit of phase of signal processing unit (5) counts corresponding horizontal measurement distance；

2) vertical direction displacement measurement：

A, third measures the second closing light signal light intensity I that light and the first reference light are formed_3-4Qiang Wei：

Wherein E₃Indicate that third measures light light vector, E₄Indicate the first reference light light vector, Φ_nIndicate the second closing light signal phase Variation, I_nIndicate the DC component of the first closing light signal light intensity signal light intensity, Δ f₂Indicate that first measures light and the second measurement optical frequency The difference of rate；

Second closing light signal phase changes Φ_nFor：

Φ_n=Φ₃+Δφ₃

Wherein Φ₃Indicate that third measures the phase change that light is generated due to measuring grating (3) horizontal motion, Δ φ₃Indicate the Three measure the phase change that light is generated due to measuring grating (3) movement in vertical direction, and：Φ₃=Φ₂；

Third measures light phase changes delta φ₃It is expressed as：

Wherein Φ_rIndicate to measure grating catenary motion component to measure the inswept one section of grid line of hot spot on grating (3) and due to The phase change of second closing light signal caused by Grating Doppler Effect,Indicate that measuring grating (3) catenary motion component makes Since laser doppler causes the phase change of the second closing light signal when along incident direction relative motion occurs for point diffraction；

B, measuring the displacement X that grating (3) vertical motion component causes hot spot inswept on grid line is：

X=x₀×Φ_r

Measuring grating (3) vertical motion component causes the optical grating diffraction point to be along the displacement L of incident direction：

And：

Wherein, θ indicates that the angle of displacement X and displacement L, α indicate Littrow angle corresponding with grating (3) are measured, x₀Indicate unit Phase count corresponds to pattern displacement,Indicate that unit of phase counts corresponding incident direction displacement, p indicates to measure the grating of grating Constant, λ are two-frequency laser shoot laser wavelength, and N is the electronic fine-grained multiple of signal processing unit (5)；

c、With Φ_rRelationship be expressed as：

Thus：

Pass throughObtain vertical deviation Δ y：

Wherein k_nIt is signal processing unit (5) to the phase count of the second closing light signal, y_resIndicate that two closing light signal phases count Unit-distance code result corresponding to movement in vertical direction distance.