An interferometric displacement measuring device based on a polarization beam splitting grating

Abstract

The application discloses an interference displacement measuring device based on a polarization beam splitting grating, which comprises a light source assembly, an optical path assembly, a photoelectric receiving module and a signal processing module; the light source assembly is used to generate a measuring light beam; the optical path assembly comprises a first reflecting prism, a reflecting grating, a second reflecting prism, a third reflecting prism and a polarization beam splitting grating; the light source assembly emits the measuring light beam to the first reflecting prism, the first reflecting prism is used to reflect the measuring light beam to the reflecting grating, the reflecting grating divides the measuring light beam into a first diffracted light and a second diffracted light, the first diffracted light and the second diffracted light are reflected to the second reflecting prism and the third reflecting prism respectively, and the second reflecting prism and the third reflecting prism are used to adjust the first diffracted light and the second diffracted light and then make the first diffracted light and the second diffracted light incident on the polarization beam splitting grating; the photoelectric receiving module is electrically connected with the signal processing module, and the signal processing module is used to perform differential calculation on a first beat frequency signal and a second beat frequency signal to calculate displacement.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of grating interferometer, and particularly relates to an interference displacement measuring device based on a polarization beam splitting grating. BACKGROUND

[0002] With the development of high-end manufacturing industry, the precision requirement of precision measurement is also higher and higher. In the field of high-precision measurement, there are currently two kinds of measurement systems. One is a laser displacement measurement system taking laser wavelength as a measurement reference. Laser wavelength is easily affected by the change of air refractive index. Because the beam transmission distance of the laser interferometer is long (more than 300 mm), even in a good working environment with good temperature and humidity control and air flow pressure control, the air flow caused by the rapid movement of the workpiece table will still cause the non-uniform distribution of the air refractive index, thereby affecting the further improvement of the positioning precision. The grating displacement measurement system takes the grating pitch as the measurement reference, which can greatly reduce the error caused by the air refractive index, and the measurement precision is from micrometer level to nanometer level or even sub-nanometer level, which provides effective technical support for the development of ultra-precision machining technology. The core component of the grating displacement measurement system is the grating, which takes the grating pitch as the reference, has compact structure, symmetrical optical path, short optical path and low sensitivity to external environment, and can be applied to multi-dimensional precision displacement measurement. From the principle, the grating displacement measurement system can be divided into zero difference type grating interference displacement measurement system and heterodyne grating interference displacement measurement system. The zero difference type grating interference displacement measurement system divides the light source into reference light and measurement light by a light splitting device, and then makes the two lights superimposed through different paths to form an interference signal that can be measured. Since the carrier frequencies of the measured light and the reference light are the same, the interference light field obtained can eliminate the influence of the frequency noise of the electromagnetic wave itself. The heterodyne grating interference displacement measurement system is a method for measuring the phase change of light. The heterodyne grating interference displacement is obtained by superimposing two light beams with slight frequency difference. The interference signal formed is a beat frequency that changes with time and phase. When displacement measurement is performed, the change information of the displacement amount is recorded in the phase of the beat frequency signal, and the required phase change can be demodulated through the corresponding demodulation technology.

[0003] The traditional heterodyne grating displacement measurement system divides the incident non-polarized light beam into two orthogonal polarized light beams by a polarization beam splitter, so as to obtain a stable interference signal. However, the polarization beam splitter is made of natural birefringent crystal or multi-layer dielectric film. The former is large and heavy, and the latter has high manufacturing cost, which is difficult to meet the requirements of the optical system. SUMMARY

[0004] The present application aims to overcome the shortcomings of the prior art, and provides an interference displacement measuring device based on a polarization beam splitting grating, which solves the problems of large size and high cost of the interference device in the prior art.

[0005] The technical scheme of the present application is: an interference displacement measurement device based on a polarization beam splitter grating, comprising a light source assembly, a light path assembly, a photoelectric receiving module and a signal processing module;

[0006] The light source assembly is used to generate two coincident, polarization orthogonal and fixed frequency difference polarization lights as measurement beams.

[0007] The light path assembly comprises a first reflecting prism, a reflective grating, a second reflecting prism, a third reflecting prism and a polarization beam splitter grating.

[0008] The light source assembly emits the measurement beams to the first reflecting prism, which is arranged on the outgoing light path of the light source assembly and is used to reflect the measurement beams to the reflective grating, the reflective grating divides the measurement beams into first and second diffracted lights, the second and third reflecting prisms are arranged on the reflected light path of the reflective grating, the first and second diffracted lights are reflected to the second and third reflecting prisms respectively, and the second and third reflecting prisms are used to adjust the first and second diffracted lights and then make them incident on the polarization beam splitter grating.

[0009] The first diffracted light generates a first S light component and a first P light component after being incident on the polarization beam splitter grating, and the second diffracted light generates a second S light component and a second P light component after being incident on the polarization beam splitter grating.

[0010] The reflective grating is arranged on the surface of a moving object, and the moving object drives the reflective grating to move along the grating vector direction Y.

[0011] The photoelectric receiving module and the signal processing module are electrically connected, the photoelectric receiving module comprises a first photoelectric detector and a second photoelectric detector, the first photoelectric receiver is used to receive the first P light component and the second S light component and generate a first beat frequency signal, the second photoelectric receiver is used to receive the second P light component and the first S light component and generate a second beat frequency signal, and the signal processing module is used to perform difference calculation on the first and second beat frequency signals to calculate the displacement.

[0012] Further, the first diffracted light is-1 order, and the second diffracted light is+1 order.

[0013] Further, the transmission optical path of the first P light component is equal to that of the second S light component, and the transmission optical path of the second P light component is equal to that of the first S light component.

[0014] Further, the polarization beam splitter grating adopts a transmission type polarization beam splitter grating structure.

[0015] Further, the second and third reflecting prisms are used to adjust the first and second diffracted lights and then make them incident on the polarization beam splitter grating at a Littrow angle.

[0016] Further, the measurement beam includes first polarized light and second polarized light, the first polarized light is P polarized light with frequency f A , and the second polarized light is S polarized light with frequency f B , the first polarized light and the second polarized light are reflected by the first reflecting prism to form first diffracted light and second diffracted light.

[0017] Further, the second reflecting prism and the third reflecting prism are oppositely and parallel arranged, the reflective grating and the polarization beam splitter are oppositely and parallel arranged, the first reflecting prism is located between the second reflecting prism and the third reflecting prism, and the second reflecting prism and the third reflecting prism are respectively located on two sides of the reflective grating and the polarization beam splitter, and the first reflecting prism is located between the reflective grating and the polarization beam splitter, and the first reflecting prism is obliquely arranged to reflect the measurement beam emitted by the light source assembly to the reflective grating.

[0018] Further, the included angle between the first reflecting prism and the reflective grating is an acute angle, and the first reflecting prism is used to make the measurement beam vertically incident to the reflective grating.

[0019] The working principle of the above interference displacement measurement device based on the polarization beam splitter is as follows:

[0020] The light source assembly is used to generate two beams of polarized light with coincident, orthogonal polarization and fixed frequency difference as the measurement beam, the measurement beam includes first polarized light and second polarized light, the first polarized light is P polarized light with frequency f A , and the second polarized light is S polarized light with frequency f B , the first polarized light and the second polarized light are reflected by the first reflecting prism to form first diffracted light and second diffracted light, the first diffracted light is incident to the polarization beam splitter to generate first S light component and first P light component, the second diffracted light is incident to the polarization beam splitter to generate second S light component and second P light component, the first photoelectric receiver is used to receive the first P light component and the second S light component and generate first beat frequency signal with frequency f A -f B , the second photoelectric receiver is used to receive the second P light component and the first S light component and generate second beat frequency signal with frequency f A -f B , the first beat frequency signal and the second beat frequency signal are respectively transmitted to the signal processing module; when the reflective grating moves along the grating vector direction, due to the grating Doppler frequency shift effect, the first diffracted light occurs negative frequency shift-Δf, and the second diffracted light occurs positive frequency shift+Δf, so that the first beat frequency signal output by the first photoelectric receiver becomes f A -f B -2Δf, and the second beat frequency signal output by the second photoelectric receiver becomes f A -fB + 2Δf, the signal processing module differentiates the first beat frequency signal and the second beat frequency signal, and realizes displacement measurement of 4 times optical subdivision of the single diffraction of the reflection grating.

[0021] Compared with the prior art, the present application has the following beneficial effects:

[0022] The present application adopts two gratings, one of which is a reflection grating, and the other is a transmission polarization beam splitting grating. The structure of the two gratings is simple and easy to mass-produce, and both are high-efficiency grating structures. The displacement measurement of 4 times optical subdivision can be realized by single diffraction of the measurement grating. This design greatly reduces the influence of grating surface accuracy and attitude error between the reading head on the measurement accuracy. The use of grating structure instead of polarization beam splitter can improve the stability of the system. Furthermore, the grating arrangement configuration used in the present application greatly improves the anti-interference ability and integration of the displacement measurement system, reduces the influence of environmental factors on the measurement system, has strong anti-interference ability, reduces the error existing in the measurement process, and improves the resolution of the measurement system. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 It is a structural schematic diagram of the interference displacement measurement device based on the polarization beam splitting grating of the present application.

[0024] Figure 2 It is a principle diagram of the transmission polarization beam splitting grating.

[0025] Light source assembly 1, measurement beam 11, first reflecting prism 2, reflection grating 3, second reflecting prism 4, third reflecting prism 5, polarization beam splitting grating 6, first photodetector 7, second photodetector 8, first diffracted light 9, first S light component 91, first P light component 92, second diffracted light 10, second S light component 101, second P light component 102, signal processing module 100. DETAILED DESCRIPTION

[0026] The present application will be further described in detail below in conjunction with the embodiments, but the embodiments of the present application are not limited thereto.

[0027] EMBODIMENT

[0028] In order to solve the problem that the optical structure of the measurement system becomes more complex by 2 times or more diffractions to realize 4 times or higher times optical subdivision in the prior art, and the grating surface accuracy and the attitude error between the grating and the reading head greatly affect the measurement accuracy.

[0029] The embodiment provides an interference displacement measurement device based on a polarization beam splitting grating, so that two polarized light beams with a fixed frequency difference emitted by a light source assembly can be diffracted once when entering a surface of a measurement grating through an optical path assembly, 4 times of optical subdivision can be realized, influence of attitude error between a grating surface precision and the optical path assembly on measurement precision can be avoided, and the optical path assembly has simple structure, small volume and light mass, and can simplify complexity of an optical structure of a measurement system.

[0030] The embodiment provides an interference displacement measurement device based on a polarization beam splitting grating, which comprises a light source assembly 1, an optical path assembly, a photoelectric receiving module and a signal processing module 100.

[0031] The light source assembly is used to generate two coincident, polarization orthogonal and fixed frequency difference polarized light beams as measurement light beams 11. A The measurement light beam comprises first polarized light and second polarized light, the first polarized light is P polarized light, and the frequency is f B .

[0032] In one embodiment, the light source assembly adopts a red light laser source.

[0033] As shown in Figure 1 , the optical path assembly comprises a first reflecting prism 2, a reflecting grating 3, a second reflecting prism 4, a third reflecting prism 5 and a polarization beam splitting grating 6.

[0034] The light source assembly 1 emits the measurement light beam to the first reflecting prism 2, the first reflecting prism 2 is arranged on an outgoing light path of the light source assembly 1, the first reflecting prism 2 is used to reflect the measurement light beam to the reflecting grating 3, the reflecting grating divides the measurement light beam into first diffracted light 9 and second diffracted light 10, the second reflecting prism and the third reflecting prism are arranged on a reflected light path of the reflecting grating, the first diffracted light and the second diffracted light are reflected to the second reflecting prism and the third reflecting prism respectively, and the second reflecting prism and the third reflecting prism are used to adjust the first diffracted light and the second diffracted light and then make the first diffracted light and the second diffracted light incident on the polarization beam splitting grating.

[0035] In one embodiment, the second reflecting prism and the third reflecting prism are oppositely and parallelly arranged, the reflecting grating and the polarization beam splitting grating are oppositely and parallelly arranged, the first reflecting prism is located between the second reflecting prism and the third reflecting prism, the second reflecting prism and the third reflecting prism are located on two sides of the reflecting grating and the polarization beam splitting grating respectively, and the first reflecting prism is located between the reflecting grating and the polarization beam splitting grating, the first reflecting prism is arranged in an inclined mode, is used to make the light source assembly emit the measurement light beam to the reflecting grating, and an included angle between the first reflecting prism and the reflecting grating is an acute angle, and the first reflecting prism is used to make the measurement light beam vertically incident on the reflecting grating.

[0036] In one embodiment, the first diffracted light is -1 order, and the second diffracted light is +1 order.

[0037] In one embodiment, the second reflective prism and the third reflective prism are used to adjust the first diffracted light and the second diffracted light to be incident on the polarization beam splitter grating at the Littrow angle.

[0038] The first diffracted light generates a first S light component 91 and a first P light component 92 after being incident on the polarization beam splitter grating, and the second diffracted light generates a second S light component 101 and a second P light component 102 after being incident on the polarization beam splitter grating.

[0039] In one embodiment, the first P light component has the same optical path as the second S light component, and the second P light component has the same optical path as the first S light component.

[0040] The optoelectronic receiving module is electrically connected to the signal processing module 100, and the optoelectronic receiving module includes a first photodetector 7 and a second photodetector 8. The first photodetector is used to receive the first P light component and the second S light component and generate a first beat frequency signal, and the second photodetector is used to receive the second P light component and the first S light component and generate a second beat frequency signal. The signal processing module is used to perform difference calculation on the first beat frequency signal and the second beat frequency signal to calculate the displacement.

[0041] In one embodiment, the polarization beam splitter grating adopts a transmissive polarization beam splitter grating structure. Figure 2 The principle diagram of the transmissive polarization beam splitter grating is shown. Taking the first diffracted light as an example, the first diffracted light is incident on the polarization beam splitter grating at the Littrow angle, and the energy of the first S light component is concentrated in the 0 order, and the energy of the first P light component is concentrated in the -1 order.

[0042] In one embodiment, the reflective grating is arranged on the surface of the moving object, and the moving object drives the reflective grating to move along the grating vector direction Y. The grating is a periodic structure, and the grating vector direction here is understood as the direction of the grating period extension.

[0043] The working principle of the above interference displacement measurement device based on the polarization beam splitter grating is as follows:

[0044] The light source assembly is used to generate two coincident, polarization orthogonal and fixed frequency difference polarization lights as measurement beams, and the measurement beams include a first polarization light and a second polarization light. The first polarization light is P polarization light, and the frequency is f A The second polarization light is S polarization light, and the frequency is f B, the first polarized light and the second polarized light are reflected by the first reflection prism to form first diffracted light and second diffracted light, the first diffracted light is incident to the polarization beam splitting grating to generate a first S light component and a first P light component, the second diffracted light is incident to the polarization beam splitting grating to generate a second S light component and a second P light component, a first photoelectric receiver is used to receive the first P light component and the second S light component and generate a first beat frequency signal with a frequency of f A -f B , a second photoelectric receiver is used to receive the second P light component and the first S light component and generate a second beat frequency signal with a frequency of f A -f B , the first beat frequency signal and the second beat frequency signal are transmitted to a signal processing module; when the reflective grating moves along the grating vector direction, due to the grating Doppler frequency shift effect, the first diffracted light has a negative frequency shift of -Δf, and the second diffracted light has a positive frequency shift of +Δf, so that the first beat frequency signal output by the first photoelectric receiver becomes f A -f B -2Δf, the second beat frequency signal output by the second photoelectric receiver becomes f A -f B +2Δf, the signal processing module differentially calculates the first beat frequency signal and the second beat frequency signal to realize the displacement measurement of 4 times optical subdivision of single diffraction of the reflective grating.

[0045] As described above, the present application can be well implemented, and the above-mentioned embodiments are only the preferred embodiments of the present application, but not to limit the scope of the present application; that is, all equivalent changes and modifications made according to the content of the present application are covered by the scope of the claims of the present application.

Claims

1. An interferometric displacement measuring device based on a polarization splitting beam splitter grating, characterized in that The light source assembly, the light path assembly, the photoelectric receiving module and the signal processing module are included. The light source assembly is used to generate two coincident, polarization orthogonal and fixed frequency difference polarized light beams as measurement light beams. The light path assembly includes a first reflecting prism, a reflective grating, a second reflecting prism, a third reflecting prism and a polarization beam splitting grating. The light source assembly emits the measurement light beams to the first reflecting prism which is arranged on the light path of the light source assembly, and the first reflecting prism is used to reflect the measurement light beams to the reflective grating. The second reflecting prism and the third reflecting prism are used to adjust the first diffraction light and the second diffraction light to be incident on the polarization beam splitting grating at the Littrow angle. The second reflecting prism and the third reflecting prism are arranged oppositely and in parallel, the reflective grating and the polarization beam splitting grating are arranged oppositely and in parallel, the first reflecting prism is located between the second reflecting prism and the third reflecting prism, the second reflecting prism and the third reflecting prism are respectively located on the two sides of the reflective grating and the polarization beam splitting grating, and the first reflecting prism is located between the reflective grating and the polarization beam splitting grating. The first reflecting prism is arranged obliquely to make the light source assembly emit the measurement light beams to the reflective grating. The first reflecting prism and the reflective grating form an acute angle, and the first reflecting prism is used to make the measurement light beams perpendicularly incident on the reflective grating. The first diffraction light generates a first S light component and a first P light component after being incident on the polarization beam splitting grating, and the second diffraction light generates a second S light component and a second P light component after being incident on the polarization beam splitting grating. The reflective grating is arranged on the surface of a moving object, and the moving object is used to drive the reflective grating to move along the direction of grating period extension. The photoelectric receiving module and the signal processing module are electrically connected, the photoelectric receiving module includes a first photoelectric detector and a second photoelectric detector, the first photoelectric receiver is used to receive the first P light component and the second S light component and generate a first beat frequency signal, and the second photoelectric receiver is used to receive the second P light component and the first S light component and generate a second beat frequency signal.

2. The polarization-dividing beam splitter grating-based interferometric displacement measurement apparatus according to claim 1, characterized by The signal processing module is used to perform difference calculation on the first beat frequency signal and the second beat frequency signal to calculate the displacement.

3. The polarization-dividing beam splitter grating-based interferometric displacement measurement apparatus according to claim 1, wherein The first diffraction light is the-1 order, and the second diffraction light is the +1 order.

4. The polarization-dividing beam splitter grating-based interferometric displacement measurement apparatus according to claim 1, characterized by, The transmission optical path of the first P light component is equal to that of the second S light component, and the transmission optical path of the second P light component is equal to that of the first S light component. The polarization beam splitting grating adopts a transmission type polarization beam splitting grating structure.

5. The polarization-dividing beam splitter grating-based interferometric displacement measurement apparatus according to claim 1, wherein The measurement beam comprises first polarized light and second polarized light, the first polarized light is P polarized light, and the frequency is f A The second polarized light is S polarized light, and the frequency is f B The first polarized light and the second polarized light are reflected by the first reflecting prism to form first diffracted light and second diffracted light.

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