CN209894118U - Displacement measurement system based on reflective single holographic grating - Google Patents

Displacement measurement system based on reflective single holographic grating Download PDF

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CN209894118U
CN209894118U CN201920395952.6U CN201920395952U CN209894118U CN 209894118 U CN209894118 U CN 209894118U CN 201920395952 U CN201920395952 U CN 201920395952U CN 209894118 U CN209894118 U CN 209894118U
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light
holographic grating
splitter prism
laser
grating
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高仁祥
李劲松
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China Jiliang University
China University of Metrology
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China University of Metrology
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Abstract

The utility model discloses a displacement measurement system based on reflection-type single holographic grating, which belongs to the field of precise displacement measurement systems and is mainly used for the precise machining industry, and comprises a laser, a collimating lens, an optical isolator, a reflector, a beam splitter prism, a polarized light beam splitter prism, a photoelectric detector, a high-density holographic grating, 1/4 wave plates, a signal conditioning system, a data acquisition card and a computer; the light beam emitted by the laser is changed through a series of phases and polarization states, so that the change of the light intensity signal received by the photoelectric detector is transmitted to the data acquisition card through the signal conditioning system and then transmitted to the computer to display the micro displacement. The utility model discloses an adopt high density holographic grating, utilize the grating pitch as the measuring basis, measurement accuracy is high, has reduced because displacement measurement error that non-orthogonality and grating location are inaccurate to be brought, reduces the influence of environment to measuring result.

Description

Displacement measurement system based on reflective single holographic grating
Technical Field
The utility model relates to a displacement measurement system based on single holographic grating of reflective belongs to accurate displacement measurement system field.
Background
With the continuous development and improvement of the scientific and technical level and the industrial production level, the detection of the micro displacement is widely applied to various fields such as precision machining, surface measurement, physical experiments and the like, and the current nanoscale high-precision measurement method can be divided into three categories according to the difference of measurement principles: microscopic measuring method, electrical measuring method and optical measuring method.
The microscope measurement method can realize high-resolution displacement measurement and can reach atomic level or even subatomic level. But the method is limited by the principle, has a small measuring range and is difficult to meet the requirement of a precise workpiece table on a large measuring range.
The electrical measurement method utilizes a capacitance sensor and an inductance sensor to convert the displacement into an electrical value, and then measures the electrical value to indirectly measure the displacement. The method has the characteristics of high resolution, simple structure and good adaptability, but the measuring range is small, and the requirement of large measuring range is difficult to meet. Chinese patent No. CN107036518A, "inductive displacement sensor fixed measurement device and measurement thereof" is known, and the measurement method of this patent is based on the change of inductance due to electromagnetic induction to generate self-inductance or mutual inductance to obtain displacement information. The disadvantages of the inductive displacement measurement method are as follows: the frequency response is low, the method is not suitable for quick dynamic measurement, the electromagnetic interference is strong, the resolution ratio and the indicating value error are related to the indicating value range, and when the indicating value range is large, the resolution ratio and the indicating value precision are correspondingly reduced.
The optical measurement method has the unique advantages in industrial application due to the characteristics of high measurement precision, non-contact, wide dynamic range, easy digitization and the like. While the laser interferometry system is widely used in industry, chinese patent No. CN105004278B, "a laser interferometry displacement measurement system" is known, wherein the measurement system obtains displacement information based on laser interferometry analysis optical path difference change. The disadvantages of the interferometric displacement measurement method are as follows: the device is easily affected by environmental changes, has large errors when the temperature, the pressure and the relative humidity are unstable, and is complex to operate.
The grating type measuring device takes stable grating distance as a measuring reference, and has the characteristics of difficult environmental interference, simple light path structure, convenient operation, low measuring device cost, suitability for finished product production, high precision and the like.
Disclosure of Invention
In order to overcome existing laser interference system with high costs, the operation is complicated, receive the big defect of environmental factor influence, the utility model provides a displacement measurement system based on reflection-type single holographic grating, its beneficial effect is:
1. and the single grating is adopted, so that the scratch caused by mutual friction of the double gratings is not needed to be worried about.
2. The adopted materials can be easily bought in the market, the cost is low, the structure is simple, and the mass production can be realized.
3. The displacement measurement system is flexible to install, convenient to adjust, high in environmental adaptability, capable of being flexibly applied to various scenes needing precision measurement and wide in application range.
In order to achieve the above purpose, the utility model discloses the technical scheme who adopts is: the displacement measuring system based on the reflective single holographic grating comprises a laser, a collimating lens, an optical isolator, a first reflecting mirror, a second reflecting mirror, a beam splitter prism, a first polarized beam splitter prism, a second polarized beam splitter prism, a third polarized beam splitter prism, a first photoelectric detector, a second photoelectric detector, a high-density holographic grating, an 1/4 wave plate, a signal conditioning system, a data acquisition card and a computer. The planes of the collimating lens, the optical isolator and the high-density holographic grating are parallel in pairs and are sequentially placed on an emergent light path of a light beam emitted by a laser, and the light beam of the laser vertically enters; the first reflector and the second reflector are respectively arranged at the +/-1-order diffraction light paths of light beams on two sides of the laser; the first polarization beam splitter prism is arranged on a reflection light path reflected by the first reflecting mirror and the second reflecting mirror, so that two beams of reflection light vertically enter two surfaces of the first polarization beam splitter prism; the 1/4 wave plate and the beam splitter prism are sequentially arranged on an emergent light path of the first polarization beam splitter prism; the second polarization beam splitter prism and the third polarization beam splitter prism are respectively arranged on two light paths emitted by the beam splitter prisms; and the first photoelectric detector and the second photoelectric detector are respectively arranged on the emergent light path of the light beam behind the second polarization beam splitter prism and the third polarization beam splitter prism.
When the laser works, a light beam emitted by the laser vertically enters the collimating lens for collimation, then vertically enters the high-density holographic grating through the optical isolator, and is diffracted through the grating. The first reflector and the second reflector are respectively arranged on + 1-order and-1-order diffraction light paths, and the + 1-order and-1-order diffraction light beams are respectively deflected through the first reflector and the second reflector at a certain angle, so that a reflected light beam vertically enters two surfaces of the first polarization beam splitter prism, the + 1-order diffraction light beam is converted into P polarized light, the-1-order diffraction light beam is converted into S polarized light, and the S polarized light beam and the L polarized light beam are converted into right-handed light and left-handed light through the 1/4 wave plates. The two beams of light are divided into two beams of light after passing through the beam splitter prism, and then pass through the second polarization beam splitter prism and the third polarization beam splitter prism respectively to obtain two paths of signals with phase differences of 90 degrees in sequence, and the two paths of signals are received by the first photoelectric detector and the second photoelectric detector respectively. And transmitting the received signals to a signal processor for processing, namely transmitting the signals to a computer for displacement analysis after passing through a signal conditioning system and a data acquisition card.
The laser is one of a solid laser, a gas laser and a fuel laser.
The light emitted by the laser is vertically emitted into the collimating lens, the optical isolator and the high-density holographic grating in sequence.
The planes of the collimating lens, the optical isolator and the high-density holographic grating are parallel to each other.
The optical isolator is an optical passive device which only allows light to pass in one direction and blocks the light from passing in the opposite direction, so that a collimation stable light source is obtained, and the phenomenon that the output power of laser is unstable due to laser feedback is avoided.
The signal conditioning system and the data acquisition card belong to signal processing, and comprise a PFI 28000 series signal conditioning module and an NI signal acquisition card.
The high-density holographic grating is characterized in that the measurement reference is grating pitch, the linear density of the high-density holographic grating is 2000/mm, namely the grating pitch is 0.5um, the high-density holographic grating is not easily influenced by the environment, and the measurement precision is greatly improved.
Description of the drawings:
FIG. 1 is a schematic structural view of the present invention;
FIG. 2 is a flow chart of a displacement measurement system based on a reflective single holographic grating;
1-a laser; 2-a collimating lens; 3-an optical isolator; 4-high density holographic grating; 5-a first mirror; 6-a second mirror; 7-a first polarized beam splitting prism; 8-1/4 wave plates; 9-beam splitter prism, 10-second polarization beam splitter prism; 11-a third polarized beam splitting prism; 12-a first photodetector; 13-a second photodetector; 14-a signal conditioning system; 15-a data acquisition card; 16-computer.
The specific implementation mode is as follows:
the utility model provides a displacement measurement system based on reflection-type diffraction single grating, it is right now to combine the figure the utility model discloses do further detailed explanation. These drawings are simplified schematic drawings and illustrate the basic structure of the present invention only in a schematic manner, and thus show only the components related to the present invention. Fig. 1 is a schematic structural diagram of a single grating displacement measurement system based on reflection diffraction, which includes: the device comprises a laser 1, a collimating lens 2, an optical isolator 3, a high-density holographic grating 4, a first reflector 5, a second reflector 6, a first polarized beam splitter prism 7, an 1/4 wave plate 8, a beam splitter prism 9, a second polarized beam splitter prism 10, a third polarized beam splitter prism 11, a first photoelectric detector 12, a second photoelectric detector 13, a signal conditioning system 14, a data acquisition card 15 and a computer 16.
The collimating lens 2, the optical isolator 3 and the high-density holographic grating 4 are sequentially arranged on an emergent light path of a light beam emitted by the laser 1. The optical isolator 3 enables the light beam emitted by the laser to completely pass through and blocks the reflected light of the high-density holographic grating, so that a collimation stable light source is obtained, and the phenomenon that the output power of the laser is unstable due to laser feedback is avoided. The first reflecting mirror 5 and the second reflecting mirror 6 are arranged on the +/-1 st order diffraction light path diffracted by the high-density holographic grating 4 and are respectively arranged on two sides of the laser 1. The first polarization beam splitter prism 7 is disposed on the reflection light path reflected by the first reflecting mirror 5 and the second reflecting mirror 6, so that two beams of reflection light vertically enter two surfaces of the first polarization beam splitter prism 7. 1/4 wave plate 8 and beam splitter prism 9 are placed in turn on the outgoing light path of the first polarization beam splitter prism 7. A second polarization beam splitter 10 and a third polarization beam splitter 11 are respectively arranged on the light paths of the two beams of light emitted by the beam splitter 9. The first photodetector 12 and the second photodetector 13 are respectively disposed on the exit planes of the second polarization beam splitter prism 10 and the third polarization beam splitter prism 11.
When the system works, the laser, the collimating lens and the optical isolator are fixed on the same plane. The light beam emitted by the laser 1 at a fixed position firstly vertically enters the collimating lens 2, the collimated light beam passes through the optical isolator 3, and the optical isolator 3 enables the light beam emitted by the laser to completely pass through to block the reflected light of the high-density holographic grating, so that the phenomenon that the output power of the laser is unstable due to laser feedback is prevented. After obtaining a stable collimated light beam, the light beam is vertically incident to the high-density holographic grating 4 on the guide rail, and is diffracted through the grating to generate +1 order and-1 order diffracted light. The first reflector 5 and the second reflector 6 are symmetrically distributed on the planes at the two sides of the laser on the diffraction light paths of + 1-order diffraction light and-1-order diffraction light, and the bottom of the reflector is provided with a knob which can be adjusted by a certain angle. The angles of the first reflecting mirror 5 and the second reflecting mirror 6 are adjusted so that +1 order and-1 order diffracted lights are incident from the center point of the reflecting mirror at a certain angle, and two beams of reflected lights are perpendicularly incident on two adjacent surfaces of the first polarization splitting prism 7.
When passing through the first polarization beam splitter prism 7, the +1 st order diffracted light is changed into P polarized light and the-1 st order diffracted light is changed into S polarized light in a specified direction because the bonding surfaces of the two right-angle prisms are coated with the polarization beam splitting dielectric film, and the vibration directions of the two beams are vertical. And the light enters 1/4 wave plate 8 vertically to become right-handed light and left-handed light, the included angle between the fast axis and the slow axis of the wave plate and the horizontal plane is 45 degrees, and the linearly polarized light with two mutually vertical vibration directions is changed into circularly polarized light with opposite rotation directions. After passing through the beam splitter prism 9, the light is split into two beams of light with equal light intensity, and then the two beams of light are respectively incident into the second polarization beam splitter prism 10 and the third polarization beam splitter prism 11, and then the vibration directions are consistent, so that interference is generated. Two paths of sinusoidal signals with the phase difference of 90 degrees can be detected on the first photoelectric detector 12 and the second photoelectric detector 13, and high-precision displacement signal measurement is achieved.
The signal received by the photodetector is transmitted to the signal processor, the signal conditioning system 14 filters noise, stabilizes the waveform, reduces the signal-to-noise ratio, obtains the waveform after stable amplification, transmits the processed signal to the data acquisition card 15, and is processed by the computer 16 for displacement analysis.
For convenience of understanding, the present invention explains the polarization state of the light beam.
The polarization state of the polarized light beam is represented by a Jones vector, and after the diffracted light passing through the first reflecting mirror passes through the second polarizing prism and the third polarizing prism, the polarization states of the diffracted light passing through the first reflecting mirror and the third reflecting mirror can be respectively represented as follows:
in the formula:the reflection coefficient of the reflecting mirror to the P polarized light and the diffraction efficiency of the grating to the P polarized light are respectively.
After the diffracted light passing through the second reflecting mirror passes through the second polarizing prism and the third polarizing prism, the polarization states of the diffracted light passing through the second reflecting mirror and the third polarizing prism can be respectively expressed as:
the electric field at the first photodetector and the second photodetector can be obtained as
Interference intensity of interference fieldIs provided withThen, there are:
and the Doppler shift of the diffraction grating is known from the knowledge of the Doppler shiftWith the speed of movement of the gratingAnd the diffraction order m, and inversely proportional to the grating pitch d, regardless of the wavelength and direction of the incident light.
Namely:
the frequency shifts of the + -1 st order diffracted lights are respectively:
the phase difference of the light intensity variation of the difference frequency interference can be obtained as follows:
in the formula: and s is the grating displacement.
From the above formula, one can obtain: the light intensity phase changes by one period for each d/2 shift of the grating. Therefore, the orthogonal light intensity signal is received by the photoelectric detector and processed, so that the signal can be resolved and counted, and the displacement of the grating movement is obtained.

Claims (4)

1. A displacement measurement system based on a reflective single holographic grating comprises a laser, a collimating lens, an optical isolator, a high-density holographic grating, a first reflector, a second reflector, a first polarized beam splitter prism, an 1/4 wave plate, a beam splitter prism, a second polarized beam splitter prism, a third polarized beam splitter prism, a first photoelectric detector, a second photoelectric detector, a signal conditioning system, a data acquisition card and a computer; the high-density holographic grating is arranged on the vertical surface of a light beam emitted by the laser and is parallel to the collimating lens and the optical isolator; the first reflector and the second reflector are positioned on two sides of the laser and symmetrically distributed on two sides of the laser; the first polarization beam splitter prism is arranged on the reflection light paths of the first reflecting mirror and the second reflecting mirror; the 1/4 wave plate is placed in the emergent light direction of the first polarization splitting prism, so that the emergent light passing through the first polarization splitting prism vertically passes through the 1/4 wave plate; the beam splitter prism divides the light beam passing through the 1/4 wave plate into two light beams with equal light intensity and vertically irradiates the second polarization beam splitter prism and the third polarization beam splitter prism respectively; the photoelectric detector receives a light intensity change signal passing through the polarized light splitting prism; the signal conditioning system, the data acquisition card and the computer condition, collect and analyze the received signals respectively.
2. The reflective single-holographic grating-based displacement measurement system of claim 1, wherein the laser emits light that is directed perpendicularly into the collimating lens, the optical isolator, and the high-density holographic grating in that order.
3. The displacement measurement system based on the reflective single holographic grating of claim 1, wherein the collimating lens, the optical isolator and the high-density holographic grating are parallel to each other.
4. The displacement measurement system based on the reflective single holographic grating of claim 1, wherein the high-density holographic grating has a linear density of 2000/mm, i.e. a pitch of 0.5 um.
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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN111207673A (en) * 2020-01-17 2020-05-29 中北大学 Displacement sensor based on isosceles triangle blazed grating structure
CN111678460A (en) * 2020-06-18 2020-09-18 中国科学院微电子研究所 Morphology measurement device and method based on spatial light splitting

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN111207673A (en) * 2020-01-17 2020-05-29 中北大学 Displacement sensor based on isosceles triangle blazed grating structure
CN111678460A (en) * 2020-06-18 2020-09-18 中国科学院微电子研究所 Morphology measurement device and method based on spatial light splitting

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