阅读说明：本技术 基于多纵模自混合效应的双正交平面镜内入射型角度传感测量装置及方法 (Incident type angle sensing measuring device and method in bi-orthogonal plane mirror based on multi-longitudinal-mode self-mixing effect ) 是由 吕亮 王晨辰 杨波 陈由泽 毕铁柱 周俊峰 于 2018-05-18 设计创作，主要内容包括：本分案申请涉及光学测量技术领域,尤其涉及一种基于多纵模自混合效应的双正交平面镜内入射型角度传感测量装置及方法,该系统包括多纵模激光器、传感单元、振动目标、滑动装置、分束器、光电探测器、信号预处理单元和信号处理单元；所述传感单元包括第一转盘、第二转盘、传动杆、相交平面镜；所述第一转盘和第二转盘通过传动杆同步转动。本装置结构简单、体积小、成本低,能够实现非接触实时高精度测量,传感单元为无源光学传感器,本身无需供电,并且测试装置光路为单光路,受环境干扰小且结构简单、调节光路方便。(The system comprises a multi-longitudinal-mode laser, a sensing unit, a vibration target, a sliding device, a beam splitter, a photoelectric detector, a signal preprocessing unit and a signal processing unit; the sensing unit comprises a first rotating disc, a second rotating disc, a transmission rod and an intersecting plane mirror; the first rotating disc and the second rotating disc synchronously rotate through the transmission rod. The device has the advantages of simple structure, small volume and low cost, can realize non-contact real-time high-precision measurement, the sensing unit is a passive optical sensor, the power supply is not required, the light path of the testing device is a single light path, the environmental interference is small, the structure is simple, and the light path is convenient to adjust.)

1. The utility model provides an incident type angle sensing measuring device in biorthogonal plane mirror based on many longitudinal modes are from mixing effect which characterized in that: the device comprises a multi-longitudinal-mode laser, a sensing unit, a vibration target, a sliding device, a beam splitter, a photoelectric detector, a signal preprocessing unit and a signal processing unit;

the sensing unit comprises a first rotating disc, a second rotating disc, a T-shaped transmission bracket, a first intersecting plane mirror, a second intersecting plane mirror, a first reflecting mirror, a second transmission rod and a third transmission rod;

the first turntable and the second turntable synchronously rotate through the T-shaped transmission bracket;

the T-shaped transmission support comprises a first transmission rod and a support rod which are horizontally arranged and are perpendicular to each other, a first connecting column and a second connecting column are connected to two ends of the first transmission rod respectively, the bottom of the first connecting column and the bottom of the second connecting column are arranged on a first rotary table and a second rotary table respectively through bearings, the first transmission rod is parallel to a connecting line between the circle center of the first rotary table and the circle center of the second rotary table, and the middle part of the support rod is connected to the second connecting column; the first intersected plane mirror comprises a first plane mirror and a second plane mirror, one side of the first plane mirror is connected with one side of the second plane mirror, and the included angle between the mirror surface of the first plane mirror and the mirror surface of the second plane mirror is 90 degrees; the second intersecting plane mirror comprises a third plane mirror and a fourth plane mirror, one side of the third plane mirror is connected with one side of the fourth plane mirror, and the included angle between the third plane mirror and the fourth plane mirror is 90 degrees; the connecting edge of the first plane mirror and the second plane mirror and the connecting edge of the third plane mirror and the fourth plane mirror are respectively connected with two ends of the supporting rod, an angular bisector of an included angle between the first plane mirror surface and the second plane mirror surface and an angular bisector of an included angle between the third plane mirror surface and the fourth plane mirror surface are both perpendicular to the supporting rod, and the mirror surfaces of the first plane mirror, the second plane mirror, the third plane mirror and the fourth plane mirror are all deviated from the first transmission rod; the first reflector is arranged in front of the first plane mirror, the included angle between the first reflector and the first plane mirror is 90 degrees, and the first reflector is fixedly connected with the first plane mirror through a second transmission rod; the second reflecting mirror is arranged in front of the fourth plane mirror, the included angle between the mirror surfaces of the second reflecting mirror and the fourth plane mirror is 90 degrees, and the second reflecting mirror is fixedly connected with the fourth plane mirror through a third transmission rod;

the vibration target can vibrate, a reflection structure is attached to a vibration surface of the vibration target, the vibration target is located in front of the third plane mirror, an included angle between the vibration surface and the plane of the third plane mirror is 45 degrees, the bottom of the vibration target is fixed on the sliding device, the vibration target can move back and forth along the direction of the laser beam incident to the vibration surface by adjusting the sliding device, and the vibration surface and the laser beam incident to the vibration surface are always kept perpendicular in the moving process;

the multi-longitudinal-mode laser emits laser beams to the second plane mirror, and the included angle between the laser beams and the second plane mirror surface is 45 degrees;

the beam splitter is arranged between the multi-longitudinal-mode laser and the second plane mirror and is used for splitting a laser beam onto the photoelectric detector;

the photoelectric detector is used for converting the received laser signal into an electric signal and then sending the electric signal to the signal preprocessing unit;

the signal preprocessing unit is used for preprocessing the received electric signals, and the preprocessing at least comprises shaping, amplifying and filtering;

the signal processing unit is used for analyzing and processing the preprocessed electric signals to obtain the rotation angles of the first rotating disc and the second rotating disc to be tested.

2. The incident type angle sensing measurement device in bi-orthogonal plane mirror based on multi-longitudinal mode self-mixing effect according to claim 1, characterized in that: and an optical attenuator is also arranged between the multi-longitudinal-mode laser and the beam splitter.

3. The incident type angle sensing measurement device in bi-orthogonal plane mirror based on multi-longitudinal mode self-mixing effect according to claim 1, characterized in that: the sliding device comprises a sliding rail and a sliding block arranged on the sliding rail, and the bottom of the vibration target is fixed on the sliding block; the slide rail and the emergent laser are positioned on the same straight line.

4. The incident type angle sensing measurement device in bi-orthogonal plane mirror based on multi-longitudinal mode self-mixing effect according to claim 1, characterized in that: the reflecting structure is a reflecting plane mirror or a reflecting film.

5. The incident type angle sensing measurement device in bi-orthogonal plane mirror based on multi-longitudinal mode self-mixing effect according to claim 1, characterized in that: the vibration target is a speaker or a piezoelectric ceramic driven by a signal generator.

6. The angle measurement method of the incident type angle sensing measurement device in the bi-orthogonal plane mirror based on the multi-longitudinal mode self-mixing effect according to claim 1, characterized in that: the vibration target vibrates, laser beams emitted by the multi-longitudinal-mode laser are incident on the vibration target through the sensing unit, the emitted laser is reflected by the reflecting structure and then fed back to the resonant cavity of the multi-longitudinal-mode laser along the original path to form a laser self-mixing signal, in the process, the turntable in the sensing unit rotates to cause the waveform of the laser self-mixing signal to change, the vibration target moves back and forth along the direction of the laser beams incident on the vibration surface by adjusting the sliding device, the vibration surface and the laser beams incident on the vibration surface are always kept vertical in the moving process to change the optical path of the vibration target from the multi-longitudinal-mode laser, so that the required laser self-mixing signals under different laser external cavity lengths are formed, the laser self-mixing signals under different laser external cavity lengths are collected by the photoelectric detector, and then the laser self-mixing signals are preprocessed by the signal preprocessing unit, and finally, analyzing the preprocessed laser self-mixing signals by using a signal processing unit to obtain the rotation angle of the turntable in the sensing unit, wherein the specific measurement and analysis method comprises the following steps:

for laser self-mixing signals of a multi-longitudinal-mode laser, different longitudinal modes of the laser only interfere with the self-mode, the finally formed laser self-mixing signals are laser self-mixing signal intensity superposition formed by the respective longitudinal modes, and according to a related interference mixing theory model, under the condition of not considering speckle influence, the multi-longitudinal-mode laser self-mixing signal intensity is obtained:

beta in the formula (1) is the total number of oscillation starting modes in the multi-longitudinal-mode laser, j represents the jth longitudinal mode in the laser, I₀Is the initial light intensity,. DELTA.I_jAmplitude of variation of light intensity of j-mode laser, phi_tjPhase, k, of the j-mode laser back and forth around the outer cavity_0jWave number, op, of j mode in vacuum_t(t) is the total optical path of the real-time external cavity of the laser, c.c. represents the complex conjugate of the formula, and the refractive index change caused by different longitudinal modes in the same material can be ignored in the calculation;

when the phase of the sensing unit changes, the external cavity total phase relationship is as follows:

phi in the formula (2)_0jInitial phase of j-mode laser back and forth one revolution of the external cavity, delta phi_sjFor sensing unit phase change, delta phi, caused by rotation angle of the turntable_cjFor compensating for phase changes, delta phi when measuring angles_sj＝-δφ_cj，op₀Is the initial optical path of the external cavity of the laser, delta op_sFor changes in the optical path of the sensing unit, delta op, caused by the angle of rotation of the turntable_cTo compensate for optical path, n_cIs the refractive index of air in the external cavity, and has a value of 1, n_sIs the refractive index of the sensing unit, and has a constant value, L_sFor the total geometrical length of the actual path of the laser light propagating in the sensor unit, L_cTo compensate for the length;

in the formula (3) < omega >₀Is the angular frequency of the laser, c is the speed of light in vacuum, n_gIs the refractive index of the laser resonant cavity medium group, L₀Is the laser resonant cavity length;

substituting formula (3) into formula (1) to obtain:

if the waveforms of the laser self-mixing signals of different modes are not separated, the waveforms of the modes need to keep the same phase or the phase delay is integral multiple of 2 pi:

φ_tj＝k_0jop_t＝2mk_0jn_gL₀＝mφ_gjformula (5)

Namely:

op_t＝2mn_gL₀formula (6)

In the formula (5), m is the external cavity mode order of the laser and is a positive integer phi_gjIs a laserThe phase of one round of round trip in the laser resonant cavity exists, so that the laser has a series of special position points, the superposed laser self-mixing signal does not generate waveform separation, and as can be known from the formula (5), when the turntable rotates for a certain angle, the phase of light during transmission of the sensing unit can be changed, and phi of each mode is caused_tjChanging m value to make m no longer be integer, separating the waveform of the superposed laser self-mixing signal, regulating slide device to change vibration target position to compensate phase change, making the waveform of the superposed laser self-mixing signal become complete waveform, measuring vibration target position to obtain compensation phase change delta phi_cjFurther obtain the phase change delta phi of the sensing unit caused by the rotation angle of the rotary table_sjHere, the angle of rotation of the turntable causes a phase change δ φ in the sensing unit_sjThe relationship of (a) is shown as follows:

in the formula (7)

using compensated phase in combination with sensing cell material refractive index n_s0Total initial geometric length L of the actual path of the laser light propagating in the sensor unit_s0The coefficient of variation of the external optical path in the sensing unit along with the angle

Technical Field

The invention relates to the technical field of optical measurement, in particular to an incident type angle sensing measurement device and method in a biorthogonal plane mirror based on a multi-longitudinal-mode self-mixing effect.

Background

The angle measurement technology is an important component of the metering technology, and with the continuous development of the scientific technology, the angle measurement technology is widely applied to the technical fields of optical-mechanical-electrical integration, aerospace, military, national defense and the like.

The angle measurement technology mainly comprises a mechanical angle measurement technology, an electromagnetic angle measurement technology and an optical angle measurement technology. In the optical angle measurement technology, the interference angle measurement technology based on the laser self-mixing theory gradually becomes an important research object for high-precision angle measurement due to the advantages of a single optical path structure, auto-collimation and the like. However, the existing angle measuring device based on the laser self-mixing theory can only realize dynamic angle measurement and cannot be applied to measurement occasions where fixed angle measurement and quantitative measurement are required.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides an angle sensing measuring device and method capable of realizing fixed angle measurement and quantitative measurement based on a multi-longitudinal-mode self-mixing effect

In order to achieve the technical purpose, the technical scheme of the invention is as follows:

an incident type angle sensing measuring device in a bi-orthogonal plane mirror based on a multi-longitudinal-mode self-mixing effect comprises a multi-longitudinal-mode laser, a sensing unit, a vibration target, a sliding device, a beam splitter, a photoelectric detector, a signal preprocessing unit and a signal processing unit;

the sensing unit comprises a first rotating disc, a second rotating disc, a T-shaped transmission bracket, a first intersecting plane mirror, a second intersecting plane mirror, a first reflecting mirror, a second transmission rod and a third transmission rod;

the first turntable and the second turntable synchronously rotate through the T-shaped transmission bracket;

the T-shaped transmission support comprises a first transmission rod and a support rod which are horizontally arranged and are perpendicular to each other, a first connecting column and a second connecting column are connected to two ends of the first transmission rod respectively, the bottom of the first connecting column and the bottom of the second connecting column are arranged on a first rotary table and a second rotary table respectively through bearings, the first transmission rod is parallel to a connecting line between the circle center of the first rotary table and the circle center of the second rotary table, and the middle part of the support rod is connected to the second connecting column; the first intersected plane mirror comprises a first plane mirror and a second plane mirror, one side of the first plane mirror is connected with one side of the second plane mirror, and the included angle between the mirror surface of the first plane mirror and the mirror surface of the second plane mirror is 90 degrees; the second intersecting plane mirror comprises a third plane mirror and a fourth plane mirror, one side of the third plane mirror is connected with one side of the fourth plane mirror, and the included angle between the third plane mirror and the fourth plane mirror is 90 degrees; the connecting edge of the first plane mirror and the second plane mirror and the connecting edge of the third plane mirror and the fourth plane mirror are respectively connected with two ends of the supporting rod, an angular bisector of an included angle between the first plane mirror surface and the second plane mirror surface and an angular bisector of an included angle between the third plane mirror surface and the fourth plane mirror surface are both perpendicular to the supporting rod, and the mirror surfaces of the first plane mirror, the second plane mirror, the third plane mirror and the fourth plane mirror are all deviated from the first transmission rod; the first reflector is arranged in front of the first plane mirror, the included angle between the first reflector and the first plane mirror is 90 degrees, and the first reflector is fixedly connected with the first plane mirror through a second transmission rod; the second reflecting mirror is arranged in front of the fourth plane mirror, the included angle between the mirror surfaces of the second reflecting mirror and the fourth plane mirror is 90 degrees, and the second reflecting mirror is fixedly connected with the fourth plane mirror through a third transmission rod;

the vibration target can vibrate, a reflection structure is attached to a vibration surface of the vibration target, the vibration target is located in front of the third plane mirror, an included angle between the vibration surface and the plane of the third plane mirror is 45 degrees, the bottom of the vibration target is fixed on the sliding device, the vibration target can move back and forth along the direction of the laser beam incident to the vibration surface by adjusting the sliding device, and the vibration surface and the laser beam incident to the vibration surface are always kept perpendicular in the moving process;

the multi-longitudinal-mode laser emits laser beams to the second plane mirror, and the included angle between the laser beams and the second plane mirror surface is 45 degrees;

the beam splitter is arranged between the multi-longitudinal-mode laser and the second plane mirror and is used for splitting a laser beam onto the photoelectric detector;

the photoelectric detector is used for converting the received laser signal into an electric signal and then sending the electric signal to the signal preprocessing unit;

the signal preprocessing unit is used for preprocessing the received electric signals, and the preprocessing at least comprises shaping, amplifying and filtering;

the signal processing unit is used for analyzing and processing the preprocessed electric signals to obtain the rotation angles of the first rotating disc and the second rotating disc to be tested.

As an improvement, an optical attenuator is also arranged between the multi-longitudinal mode laser and the beam splitter.

As an improvement, the sliding device comprises a sliding rail and a sliding block arranged on the sliding rail, and the bottom of the vibration target is fixed on the sliding block; the slide rail and the emergent laser are positioned on the same straight line;

as an improvement, the reflecting structure is a reflecting plane mirror or a reflecting film.

As a refinement, the vibration target is a speaker or a piezoelectric ceramic driven by a signal generator.

The angle measurement method of the incident type angle sensing measurement device in the biorthogonal plane mirror based on the multi-longitudinal-mode self-mixing effect comprises the following steps: the vibration target vibrates, laser beams emitted by the multi-longitudinal-mode laser are incident on the vibration target through the sensing unit, the emitted laser is reflected by the reflecting structure and then fed back to the resonant cavity of the multi-longitudinal-mode laser along the original path to form a laser self-mixing signal, in the process, the turntable in the sensing unit rotates to cause the waveform of the laser self-mixing signal to change, the vibration target moves back and forth along the direction of the laser beams incident on the vibration surface by adjusting the sliding device, the vibration surface and the laser beams incident on the vibration surface are always kept vertical in the moving process to change the optical path of the vibration target from the multi-longitudinal-mode laser, so that the required laser self-mixing signals under different laser external cavity lengths are formed, the laser self-mixing signals under different laser external cavity lengths are collected by the photoelectric detector, and then the laser self-mixing signals are preprocessed by the signal preprocessing unit, and finally, analyzing the preprocessed laser self-mixing signals by using a signal processing unit to obtain the rotation angle of the turntable in the sensing unit, wherein the specific measurement and analysis method comprises the following steps:

for laser self-mixing signals of a multi-longitudinal-mode laser, different longitudinal modes of the laser only interfere with the self-mode, the finally formed laser self-mixing signals are laser self-mixing signal intensity superposition formed by the respective longitudinal modes, and according to a related interference mixing theory model, under the condition of not considering speckle influence, the multi-longitudinal-mode laser self-mixing signal intensity is obtained:

beta in the formula (1) is the total number of oscillation starting modes in the multi-longitudinal-mode laser, j represents the jth longitudinal mode in the laser, I₀Is the initial light intensity,. DELTA.I_jAmplitude of variation of light intensity of j-mode laser, phi_tjPhase, k, of the j-mode laser back and forth around the outer cavity_0jWave number, op, of j mode in vacuum_t(t) is the total optical path of the real-time external cavity of the laser, c.c. represents the complex conjugate of the formula, and the refractive index change caused by different longitudinal modes in the same material can be ignored in the calculation;

when the phase of the sensing unit changes, the external cavity total phase relationship is as follows:

phi in the formula (2)_0jInitial phase of j-mode laser back and forth one revolution of the external cavity, delta phi_sjFor sensing unit phase change, delta phi, caused by rotation angle of the turntable_cjFor compensating for phase changes, delta phi when measuring angles_sj＝-δφ_cj，op₀Is the initial optical path of the external cavity of the laser, delta op_sFor changes in the optical path of the sensing unit, delta op, caused by the angle of rotation of the turntable_cTo compensate for optical path, n_cIs the refractive index of air in the external cavity, and has a value of 1, n_sIs the refractive index of the sensing unit, and has a constant value, L_sFor the total geometrical length of the actual path of the laser light propagating in the sensor unit, L_cTo compensate for the length;

in the formula (3) < omega >₀Is the angular frequency of the laser, c is the speed of light in vacuum, n_gIs the refractive index of the laser resonant cavity medium group, L₀Is the laser resonant cavity length;

substituting formula (3) into formula (1) to obtain:

if the waveforms of the laser self-mixing signals of different modes are not separated, the waveforms of the modes need to keep the same phase or the phase delay is integral multiple of 2 pi:

φ_tj＝k_0jop_t＝2mk_0jn_gL₀＝mφ_gjformula (5)

Namely:

op_t＝2mn_gL₀formula (6)

In the formula (5), m is the external cavity mode order of the laser and is a positive integer phi_gjThe laser has a phase of one round trip in the resonant cavity of the laser, so that the laser has a series of special position points to enable the superposed laser to be self-mixedThe signal does not produce waveform separation. As can be seen from equation (5), when the turntable rotates a certain angle, the phase of the light transmitted by the sensing unit changes, resulting in phi of each mode_tjChanging m value to make m no longer be integer, separating the waveform of the superposed laser self-mixing signal, regulating slide device to change vibration target position to compensate phase change, making the waveform of the superposed laser self-mixing signal become complete waveform, measuring vibration target position to obtain compensation phase change delta phi_cjFurther obtain the phase change delta phi of the sensing unit caused by the rotation angle of the rotary table_sjHere, the angle of rotation of the turntable causes a phase change δ φ in the sensing unit_sjThe relationship of (a) is shown as follows:

in the formula (7)

Is the coefficient of variation of external optical path with angle, L, in the sensing unit_s0For the total initial geometric length of the actual path of the laser light propagating in the sensor unit, n_s0Is the refractive index of the sensing unit material;

using compensated phase in combination with sensing cell material refractive index n_s0Total initial geometric length L of the actual path of the laser light propagating in the sensor unit_s0The coefficient of variation of the external optical path in the sensing unit along with the angle

And calculating to obtain the rotation angle of the rotary disc in the sensing unit.

From the above description, it can be seen that the present invention has the following advantages:

1. the sensing unit of the measuring device is a passive optical sensor, and power supply is not needed;

2. the test device has smaller volume and lower cost;

3. non-contact real-time high-precision measurement can be realized;

4. the optical path of the measuring device is a single optical path, the measuring device is small in environmental interference, simple in structure and convenient to adjust the optical path;

5. the sensitivity and resolution of angle measurement can be adjusted by designing parameters of the sensing unit and selecting different external cavity measuring tools.

Drawings

FIG. 1 is a schematic structural view of embodiment 1 of the present invention;

FIG. 2 is a schematic structural view of embodiment 1 of the present invention;

FIG. 3 is a schematic diagram of the optical path structure of an arbitrary-angle intersecting plane mirror in example 1 of the present invention;

FIG. 4 is a diagram showing simulation results of embodiment 1 of the present invention;

FIG. 5 is a diagram showing simulation results of embodiment 1 of the present invention;

FIG. 6 is a schematic structural view of embodiment 2 of the present invention;

FIG. 7 is a schematic structural view of embodiment 2 of the present invention;

FIG. 8 is a schematic diagram of the optical path structure of a single orthogonal plane mirror in example 2 of the present invention;

FIG. 9 is a schematic diagram of the optical path structure of a bi-orthogonal plane mirror in example 2 of the present invention;

fig. 10 is a diagram showing simulation results of embodiment 2 of the present invention.

Detailed Description

Embodiment 1 of the present invention is described in detail with reference to fig. 1 to 5, but the present invention is not limited to the claims.

As shown in fig. 1, an angle sensing and measuring device based on a multi-longitudinal-mode self-mixing effect includes a multi-longitudinal-mode laser 1, a sensing unit 2, a vibrating target 3, a sliding device 4, a beam splitter 5, a photodetector 6, a signal preprocessing unit 7 and a signal processing unit 8; the sensing unit 2 comprises a first rotating disc 211, a second rotating disc 212, a transmission rod 213 and an intersecting plane mirror 214, wherein the first rotating disc 211 and the second rotating disc 212 synchronously rotate through the transmission rod 213, the end parts of the two ends of the transmission rod 213 are respectively connected with a first connecting column 215 and a second connecting column 216, and the bottom of the first connecting column 215 and the bottom of the second connecting column 216 are respectively arranged on the first rotating disc 211 and the second rotating disc 211 through bearingsOn the second turntable 212, the transmission rod 213 is parallel to the connection line between the center of the first turntable 211 and the center of the second turntable 212, the intersecting plane mirror 214 includes a first plane mirror 2141 and a second plane mirror 2142 with mirror surfaces facing each other, one side of the first plane mirror 2141 is connected to one side of the second plane mirror 2142, the connection edges of the two are connected to the second connection column 216, the mirror surfaces of the first plane mirror 2141 and the second plane mirror 2142 are both deviated from the transmission rod 213, the angular bisector of the included angle between the mirror surfaces of the first plane mirror 2141 and the second plane mirror 2142 is located on the same straight line with the transmission rod 213, the included angle between the mirror surfaces of the first plane mirror 2141 and the second plane mirror 2142 is recorded as α, and the value range of α is: 0 degree<α<180 degrees; the vibrating target 3 can vibrate, a reflecting structure is attached to the vibrating surface of the vibrating target 3, the vibrating target 3 is arranged outside the second plane mirror 2142, and the included angle between the vibrating surface and the mirror surface of the first plane mirror 2141 is equal to

The bottom of the vibration target 3 is fixed on a sliding device 4, the vibration target 3 can move back and forth along the direction of the laser beam incident on the vibration surface by adjusting the sliding device 4, and the vibration surface is always vertical to the laser beam incident on the vibration surface in the moving process; the multi-longitudinal-mode laser 1 emits laser beams onto the second plane mirror 2142, and the included angle between the laser beams and the second plane mirror 2142 is

The included angle formed by the laser beams emitted by the multi-longitudinal-mode laser 1 and the laser beams reflected by the second plane mirror 2142 is equal to alpha, and the included angle between the laser beams emitted by the multi-longitudinal-mode laser and the vibration surface of the vibration target is equal to alpha

The beam splitter 5 is arranged between the multi-longitudinal-mode laser 1 and the second plane mirror 2142 and is used for splitting the laser beam to the photoelectric detector 6; the photoelectric detector 6 is used for converting the received laser signal into an electric signal and then sending the electric signal to the signal preprocessing unit 7; the signal preprocessing unit 7 is used for preprocessing the received electric signalsThe preprocessing at least comprises shaping, amplifying and filtering; the signal processing unit 8 is configured to analyze the preprocessed electrical signals to obtain rotation angles of the first rotating disk 211 and the second rotating disk 212 to be tested.

The angle measuring method based on the measuring device comprises the following steps: the vibration target vibrates, the laser beam emitted by the multi-longitudinal mode laser is reflected to the second plane mirror, then reflected to the first plane mirror and then reflected to the vibration target, the laser beam incident to the vibration target is reflected by the reflection structure, the reflected beam is fed back to the resonant cavity of the multi-longitudinal mode laser along the original path to form a laser self-mixing signal, in the process, any rotating disc in the sensing unit rotates (the first rotating disc and the second rotating disc can synchronously rotate based on the arrangement of the transmission rod, when any rotating disc rotates, the transmission rod drives the other rotating disc to synchronously rotate), the intersecting plane mirror is driven to horizontally move to change the waveform of the laser self-mixing signal, the vibration target moves back and forth along the direction of the laser beam incident to the vibration surface by adjusting the sliding device, and the vibration surface and the laser beam incident to the vibration surface are always kept vertical in the moving process, the method comprises the following steps of changing the optical path of a multi-longitudinal-mode laser at a vibration target distance to form required laser self-mixing signals under different laser external cavity lengths, collecting the laser self-mixing signals under the different laser external cavity lengths by using a photoelectric detector, preprocessing the laser self-mixing signals by using a signal preprocessing unit, and analyzing the preprocessed laser self-mixing signals by using a signal processing unit to obtain the rotation angle of a turntable in a sensing unit, wherein the specific measurement and analysis method comprises the following steps:

for laser self-mixing signals of a multi-longitudinal-mode laser, different longitudinal modes of the laser only interfere with the self-mode, the finally formed laser self-mixing signals are laser self-mixing signal intensity superposition formed by the respective longitudinal modes, and according to a related interference mixing theory model, under the condition of not considering speckle influence, the multi-longitudinal-mode laser self-mixing signal intensity is obtained:

beta in the formula (1) is the total number of oscillation starting modes in the multi-longitudinal-mode laser, j represents the jth longitudinal mode in the laser, I₀Is the initial light intensity,. DELTA.I_jAmplitude of variation of light intensity of j-mode laser, phi_tjPhase, k, of the j-mode laser back and forth around the outer cavity_0jWave number, op, of j mode in vacuum_t(t) is the total optical path of the real-time external cavity of the laser, c.c. represents the complex conjugate of the formula, and the refractive index change caused by different longitudinal modes in the same material can be ignored in the calculation;

when the phase of the sensing unit changes, the external cavity total phase relationship is as follows:

phi in the formula (2)_0jInitial phase of j-mode laser back and forth one revolution of the external cavity, delta phi_sjFor sensing unit phase change, delta phi, caused by rotation angle of the turntable_cjFor compensating for phase changes, delta phi when measuring angles_sj＝-δφ_cj，op₀Is the initial optical path of the external cavity of the laser, delta op_sFor changes in the optical path of the sensing unit, delta op, caused by the angle of rotation of the turntable_cTo compensate for optical path, n_cIs the refractive index of air in the external cavity, and has a value of 1, n_sIs the refractive index of the sensing unit, and has a constant value, L_sFor the total geometrical length of the actual path of the laser light propagating in the sensor unit, L_cTo compensate for the length;

in the formula (3) < omega >₀Is the angular frequency of the laser, c is the speed of light in vacuum, n_gIs the refractive index of the laser resonant cavity medium group, L₀Is the laser resonant cavity length;

substituting formula (3) into formula (1) to obtain:

if the waveforms of the laser self-mixing signals of different modes are not separated, the waveforms of the modes need to keep the same phase or the phase delay is integral multiple of 2 pi:

φ_tj＝k_0jop_t＝2mk_0jn_gL₀＝mφ_gjformula (5)

Namely:

op_t＝2mn_gL₀formula (6)

In the formula (5), m is the external cavity mode order of the laser and is a positive integer phi_gjThe laser has a series of special position points for the phase of the laser which makes the laser self-mixing signal after being superimposed not generate waveform separation. As can be seen from equation (5), when the turntable rotates a certain angle, the phase of the light transmitted by the sensing unit changes, resulting in phi of each mode_tjChanging m value to make m no longer be integer, separating the waveform of the superposed laser self-mixing signal, regulating slide device to change vibration target position to compensate phase change, making the waveform of the superposed laser self-mixing signal become complete waveform, measuring vibration target position to obtain compensation phase change delta phi_cjFurther obtain the phase change delta phi of the sensing unit caused by the rotation angle of the rotary table_sjHere, the angle of rotation of the turntable causes a phase change δ φ in the sensing unit_sjThe relationship of (a) is shown as follows:

in the formula (7)

Is the coefficient of variation of external optical path with angle, L, in the sensing unit_s0For the total initial geometric length of the actual path of the laser light propagating in the sensor unit, n_s0Is the refractive index of the sensing unit material;

using compensating phase in combination with sensing elementsRefractive index n of the material_s0Total initial geometric length L of the actual path of the laser light propagating in the sensor unit_s0The coefficient of variation of the external optical path in the sensing unit along with the angle

And calculating to obtain the rotation angle of the rotary disc in the sensing unit.

The external cavity change sensitivity S of the angle sensor can be further obtained by the formula (7)_mLcAnd adjacent order angle difference delta theta_m. Wherein the external cavity variation sensitivity S_mLcMeans the length change of the compensation external cavity caused by the change of unit angle and the angle difference delta theta of adjacent level_mRefers to the angle theta₂Position (m +1 level) and angle theta of external cavity equiphase point caused by (after change)₁And (before change) the adjacent-level angle difference corresponding to the position (m level) of the external cavity equiphase point. In general, in the angle measurement process, if the measured angle difference in two consecutive measurement intervals is greater than the adjacent-stage angle difference Δ θ_mThe number of cycles of the waveform change of the self-mixing signal, i.e. the change of the value m, in two consecutive measurement intervals is recorded, and the length of the compensation external cavity is adjusted to restore the waveform of the laser self-mixing signal to the position where the waveform of the signal corresponding to the mth level coincides.

The external cavity variation sensitivity S is expressed by the formulas (8) and (9), respectively_mLcAnd adjacent order angle difference delta theta_mExpression:

in the above measurement and analysis method, the analysis method of the relationship between the external optical path of the sensing unit and the angle change is as follows:

as shown in fig. 2, a start position O₂V (i.e. the center O of the second turntable)₂A line connecting the fixed points V of the intersecting plane mirrors) is parallel to the y-axis, and when the rotation angle of the first rotating disc 1 is theta

The second turntable 2 rotates by the same angle, and the transmission rod is always parallel to the x axis to ensure that the intersecting plane mirror does not deviate in the vertical direction and only generates translation in the xy plane. After the rotation, the first plane mirror and the second plane mirror are both crossed and shifted, the laser 1 emits laser through the point A, in the whole rotation process, the position of the laser 1 is always kept at the point A, light rays are reflected by the plane mirror and the reflector for multiple times and then return from the point D along the original path, and the radiuses of the first rotary disc and the second rotary disc are both R.

Based on the angle measurement system with the single-intersection plane mirror, the optical path change of the angle measurement system is theoretically calculated, a single intersection plane mirror structure diagram with any included angle as shown in figure 3 is established, and the vertex V of the intersection plane mirror₁Reaches V after rotating₂Primary light path AB₁C₁D₁Become AB₂C₂D₂The optical path difference can be derived as follows:

wherein the content of the first and second substances,

geometrically derived:

the optical path difference caused by the angle change can be expressed as:

substituting equation (7) yields:

combining the formula (12), it can be known that the optical path difference is related to the included angle α between the two mirror surfaces and the rotation angle θ of the turntable, and the included angle between the special mirror surfaces is simplified as follows for the simplified equation:

(1) when the included angle alpha of the two mirror surfaces is 90 degrees, namely the two mirror surfaces are vertical, the optical path difference can be obtained:

ΔL＝-4Rsinθ (14)

in this case, formula (14) is substituted into formulae (7), (8), and (9) to obtain:

δφ_sj＝k_0jn_s0|-4Rsinθ|＝-k_0jδ(n_cL_c)＝-δφ_cj (15)

the experimental device is established based on the technical scheme, the experimental device adopts the dual-mode LD laser as a light source, simulation software is utilized for analog simulation, and for simplicity, only the intensity superposition waveform of the dual-mode LD laser self-mixing signal with the same amplitude is considered. The simulation results are shown in fig. 4. As can be seen from FIG. 4, when the angle is 0, the initial external cavity optical length of the laser is 1050mm and n_gL₀M is 1000, and the laser self-mixing signal waveform is not separated. When the angle of the sensing unit increases

When the phase of a sensing unit is slightly changed, the waveform of overlapped laser self-mixing signals is separated, the length of a fine-tuning compensation external cavity is 18.15mm, and the external cavity phase of the laser becomes phi again_gThe overlapped laser wave shape disappears separately from the mixed signal wave shape, and finally the change of the corresponding sensing unit angle is obtained by measuring the compensation phase, thereby realizing the measurement of the rotating angle of the sensing unit turntable.

(2) When the included angle α of the mirror surface is 60 °, the optical path difference can be obtained:

in this case, by substituting equation (18) into equations (7), (8), and (9):

the experimental device is established based on the technical scheme, the experimental device adopts the dual-mode LD laser as a light source, simulation software is utilized for analog simulation, and for simplicity, only the intensity superposition waveform of the dual-mode LD laser self-mixing signal with the same amplitude is considered. The simulation diagram is shown in fig. 5. As can be seen from FIG. 5, when the angle is 0, the initial external cavity optical length of the laser is 1050mm and n_gL₀M is 1000, and the laser self-mixing signal waveform is not separated. When the angle of the sensing unit increases

When the laser self-mixing signal waveform is separated, the length of a fine-tuning compensation external cavity is 0.28mm, and the external cavity phase of the laser becomes phi again_gThe overlapped laser wave shape disappears separately from the mixed signal wave shape, and finally the change of the corresponding sensing unit angle is obtained by measuring the compensation phase, thereby realizing the measurement of the rotating angle of the sensing unit turntable.

It can be seen from the derivation process that, compared with the conventional laser self-mixing angle measurement method, the incident type self-mixing angle measurement system and measurement method in the single arbitrary angle intersection plane mirror described in this embodiment have the advantages that the angle measurement range is not limited, and the system resolution is higher.

As can be seen from the above description, the present embodiment has the following advantages:

1. the sensing unit of the measuring device is a passive optical sensor, and power supply is not needed;

2. the test device has smaller volume and lower cost;

3. non-contact real-time high-precision measurement can be realized;

4. the optical path of the measuring device is a single optical path, the measuring device is small in environmental interference, simple in structure and convenient to adjust the optical path;

5. the sensitivity and the resolution of angle measurement can be adjusted by designing and selecting different external cavity measuring tools through parameters of the sensing unit;

6. the structure of the sensing unit is as follows: (1) when laser beams are incident to the intersecting plane mirrors, the laser beams are firstly incident to the second plane mirror on the inner side, namely, an internal incidence mode is adopted, so that the overall structure of the measuring system is compact; (2) through the reflection unit formed by the intersecting plane mirror and the vibration target, the auto-collimation of the laser self-mixing signal is realized, and compared with the reflection unit formed by the traditional plane mirror or the reflection unit formed by a right-angle prism, the optical path difference of the laser self-mixing signal is increased before and after rotation under the same rotation angle, so that the measurement resolution and the measurement range of the system are improved; (3) the whole structure of the measuring system is simple and easy to realize, the mechanical error is small, the included angle between the first plane mirror and the second plane mirror is adjustable, different angles correspond to different system measurement resolutions, and the included angle can be selected according to actual requirements.

Embodiment 2 of the present invention will be described in detail with reference to fig. 6 to 10, but the present invention is not limited to the claims.

As shown in fig. 6, an angle sensing and measuring device based on a multi-longitudinal-mode self-mixing effect includes a multi-longitudinal-mode laser 1, a sensing unit 2, a vibrating target 3, a sliding device 4, a beam splitter 5, a photodetector 6, a signal preprocessing unit 7, and a signal processing unit 8;

the sensing unit 2 comprises a first rotating disc 231, a second rotating disc 232, a T-shaped transmission bracket, a first crossed plane mirror, a second crossed plane mirror, a first reflecting mirror 236, a second reflecting mirror 237, a second transmission rod 238 and a third transmission rod 239, wherein the first rotating disc 231 and the second rotating disc 232 synchronously rotate through the T-shaped transmission bracket 233, the T-shaped transmission bracket comprises a first transmission rod 2331 and a support rod 2332 which are horizontally arranged and are perpendicular to each other, two ends of the first transmission rod 2331 are respectively connected with a first connecting column 240 and a second connecting column 241, the bottom of the first connecting column 240 and the bottom of the second connecting column 241 are respectively arranged on the first rotating disc 231 and the second rotating disc 232 through bearings, the first transmission rod 2331 is parallel to a connecting line between the circle center of the first rotating disc 231 and the circle center of the second rotating disc 232, and the middle part of the support rod 2332 is connected to; the first intersected plane mirror comprises a first plane mirror 2341 and a second plane mirror 2342, one side of the first plane mirror 2341 is connected with one side of the second plane mirror 2342, and an included angle between the mirror surface of the first plane mirror 2341 and the mirror surface of the second plane mirror 2342 is 90 degrees; the second intersecting plane mirrors include a third plane mirror 2351 and a fourth plane mirror 2352, one side of the third plane mirror 2351 is connected with one side of the fourth plane mirror 2352, an included angle between the mirror surface of the third plane mirror 2351 and the mirror surface of the fourth plane mirror 2352 is 90 degrees, a connecting edge of the first plane mirror 2341 and the second plane mirror 2342 and a connecting edge of the third plane mirror 2351 and the fourth plane mirror 2352 are respectively connected with two ends of the support rod 2332, an angular bisector of an included angle between the mirror surface of the first plane mirror 2341 and the second plane mirror 2342 and an angular bisector of an included angle between the mirror surface of the third plane mirror 2351 and the mirror surface of the fourth plane mirror 2352 are perpendicular to the support rod 2332, the first plane mirror 2341 and the second plane mirror 2342, the mirror surfaces of the third flat mirror 2351 and the fourth flat mirror 2352 are both deviated from the first transmission rod 2331, the first reflecting mirror 236 is arranged in front of the first flat mirror 2341, the included angle between the mirror surfaces is 90 degrees, and the first reflecting mirror 236 is fixedly connected with the first flat mirror 2341 through the second transmission rod 238; the second reflecting mirror 237 is arranged in front of the fourth plane mirror 2352, and the included angle between the two mirror surfaces is 90 degrees, and the second reflecting mirror 237 is fixedly connected with the fourth plane mirror 2352 through a third transmission rod 239; the vibration target 3 can vibrate, a reflection structure is attached to a vibration surface of the vibration target 3, the vibration target 3 is located in front of the third plane mirror 2351, an included angle between the vibration surface and the mirror surface of the third plane mirror 2351 is 45 degrees, the bottom of the vibration target 3 is fixed on the sliding device 4, the vibration target 3 can move back and forth along the direction of a laser beam incident on the vibration surface by adjusting the sliding device 4, and the vibration surface and the laser beam incident on the vibration surface are always kept perpendicular in the moving process; the multi-longitudinal-mode laser 1 emits laser beams to the second plane mirror 2342, and an included angle between the laser beams and the mirror surface of the second plane mirror 2342 is 45 degrees; the beam splitter 5 is arranged between the multi-longitudinal-mode laser 1 and the second plane mirror 2342 and is used for splitting a laser beam onto the photoelectric detector 6; the photoelectric detector 6 is used for converting the received laser signal into an electric signal and then sending the electric signal to the signal preprocessing unit 7; the signal preprocessing unit 7 is used for preprocessing the received electric signals, and the preprocessing at least comprises shaping, amplifying and filtering; the signal processing unit 8 is used for analyzing and processing the preprocessed electric signals to obtain the rotation angles of the first rotating disk and the second rotating disk to be tested.

The angle measuring method based on the measuring device comprises the following steps: the vibration target vibrates, the laser beam emitted by the multi-longitudinal mode laser enters the second plane mirror at an angle of 45 degrees, the laser beam is reflected to the first reflecting mirror through the first plane mirror, the laser beam is reflected to the second reflecting mirror through the first reflecting mirror and then reflected to the fourth plane mirror through the second reflecting mirror, the direction of the laser beam entering the fourth plane mirror is the same as the direction of the laser beam emitted by the laser, the included angle between the laser beam and the fourth plane mirror is 45 degrees, the laser beam is sequentially reflected through the mutually vertical fourth plane mirror and the third plane mirror and then enters the vibration target at an angle of 90 degrees, the laser beam entering the vibration target is opposite to the direction of the laser beam emitted by the laser and is reflected by the reflecting structure, the reflected beam is fed back to the resonant cavity of the multi-longitudinal mode laser along the original path to form a laser self-mixing signal, in the process, any rotating disc in the sensing unit rotates (the first rotating disc and the second rotating disc can synchronously rotate based on, when any one turntable rotates, the T-shaped transmission bracket drives the other turntable to synchronously rotate) to drive the first intersecting plane mirror and the second intersecting plane mirror to horizontally move, so that the waveform of the laser self-mixing signal is changed, the vibration target is moved back and forth along the direction of the laser beam incident on the vibration surface by adjusting the sliding device, the vibration surface and the laser beam incident on the vibration surface are always vertical in the moving process to change the optical path of the vibration target from the multi-longitudinal-mode laser, so that the required laser self-mixing signals under different laser external cavity lengths are formed, the laser self-mixing signals under different laser external cavity lengths are collected by the photoelectric detector, then the laser self-mixing signals are preprocessed by the signal preprocessing unit, and finally the preprocessed laser self-mixing signals are analyzed by the signal processing unit, the rotation angle of the rotary disc in the sensing unit can be obtained.

The specific measurement and analysis method of this embodiment is the same as the measurement and analysis method in embodiment 1, and referring to the analysis processes from formula (1) to formula (9), the difference between this embodiment and embodiment 1 is only that the specific structure of the sensing unit is different, so that the relationship between the external optical path and the angle change of the sensing unit in this embodiment is different from the relationship in embodiment 1.

In this embodiment, the method for analyzing the relationship between the external optical path of the sensing unit and the angle change is as follows:

as shown in FIG. 7, a start position P₁P₂(first orthogonal plane mirror 4 vertex P₁And the vertex P of the second orthogonal plane mirror₂Is parallel to the y-axis, when the first rotation angle is theta

The second turntable rotates by the same angle, and the T-shaped transmission support is always parallel to the x axis so as to ensure that the first orthogonal plane mirror and the second orthogonal plane mirror do not deviate in the vertical direction and only generate translation in the xy plane. After the rotation, the first plane mirror, the second plane mirror, the third plane mirror and the fourth plane mirror are mutually orthogonal and generate deviation, the laser device emits laser light through the point A, in the whole rotation process, the position of the laser device is always kept at the point A, the light returns from the point H along the original path after being reflected by the plane mirrors and the reflectors for multiple times, and the radiuses of the first rotary disc and the second rotary disc are both R. The first intersecting plane mirror and the second intersecting plane mirror are orthogonal plane mirrors due to the fact that the included angle is 90 degrees.

Based on the angle measurement system with the double orthogonal plane mirrors, the optical path change of the angle measurement system is theoretically calculated, the experimental device is simplified, and the structural diagram of the single orthogonal plane mirror shown in fig. 8 is established.

As shown in FIG. 8, the vertex V of the orthogonal plane mirror₁Reaches V after rotating₂Primary light path AB₁C₁D₁Become AB₂C₂D₂The optical path difference can be derived as follows:

Δl＝-2(AB₁C₁D₁-AB₂C₂D₂) (22)

by geometric derivation, the optical path difference caused by the angle change can be represented as:

Δl＝-4Rsinθ (23)

therefore, for the angle measurement system with the biorthogonal plane mirrors described in this embodiment, as shown in fig. 9, the optical path difference can be calculated as:

in this case, by substituting equation (24) into equations (7), (8), and (9):

δφ_sj＝k_0jn_s0|2R(2sinθ-cosθ+1)|＝-k_0jδ(n_cL_c)＝-δφ_cj (25)

the experimental device is established based on the technical scheme, the experimental device adopts the dual-mode LD laser as a light source, simulation software is utilized for analog simulation, and for simplicity, only the intensity superposition waveform of the dual-mode LD laser self-mixing signal with the same amplitude is considered. The simulation results are shown in fig. 10. As can be seen from FIG. 10, when the angle is 0, the external cavity initial optical path of the laser is 1050mm and n_gL₀M is 1000, and the laser self-mixing signal waveform is not separated. When the angle of the sensing unit increasesWhen the phase of the sensing unit slightly changes, the overlapped laser self-mixing signal waveform is separated, the length of the fine-tuning compensation external cavity is 13.34mm, and the external cavity phase of the laser becomes phi again_gThe overlapped laser wave shape disappears separately from the mixed signal wave shape, and finally the change of the corresponding sensing unit angle is obtained by measuring the compensation phase, thereby realizing the measurement of the rotating angle of the sensing unit turntable.

It can be seen from the derivation process that, compared with the conventional laser self-mixing angle measurement method, the incident type laser self-mixing angle measurement system and measurement method in the biorthogonal plane mirror described in this embodiment have the advantages of unlimited angle measurement range and high system resolution.

As can be seen from the above description, the present embodiment has the following advantages:

1. the sensing unit of the measuring device is a passive optical sensor, and power supply is not needed;

2. the test device has smaller volume and lower cost;

3. non-contact real-time high-precision measurement can be realized;

4. the optical path of the measuring device is a single optical path, the measuring device is small in environmental interference, simple in structure and convenient to adjust the optical path;

5. the sensitivity and the resolution of angle measurement can be adjusted by designing and selecting different external cavity measuring tools through parameters of the sensing unit;

6. the structure of the sensing unit is as follows: (1) when laser beams are incident to the first intersecting plane mirror, the laser beams are firstly incident to the second plane mirror at the inner side, namely, an internal incidence mode is adopted, so that the whole structure of the measuring system is compact; (2) through the reflection unit formed by the first orthogonal plane mirror, the first reflection mirror, the second orthogonal plane mirror and the third reflection mirror, the auto-collimation of the laser self-mixing signal is realized, and compared with the reflection unit formed by the traditional plane mirror or the reflection unit formed by a right-angle prism, the optical path difference of the laser self-mixing signal is increased before and after rotation under the same rotation angle, so that the measurement resolution and the measurement range of the system are improved; (3) the measuring system linkage device is simple and easy to realize; the two external reflectors are separately linked and can be independently controlled, so that the machining error is reduced, and the light path is more easily collimated.

In the two embodiments, the measuring device may be optimized or improved as follows:

1. preferably, in an embodiment with two rotating discs, a driving belt is sleeved on the first rotating disc and the second rotating disc, and the two rotating discs rotate synchronously through the driving belt;

2. preferably, the sliding device 4 includes a sliding rail 41 and a sliding block 42 disposed on the sliding rail 41, and the bottom of the vibration target is fixed on the sliding block 42; the slide rail 41 is in the same straight line with the direction of the laser beam incident to the vibration surface of the vibration target;

3. preferably, the reflecting structure may be a reflecting plane mirror, or may be a material having scattering properties or reflecting properties, such as a reflecting film;

4. preferably, the vibration target 3 can adopt a loudspeaker 32 driven by a signal generator 31 or piezoelectric ceramics, two loudspeakers 32 in fig. 1 and 6 respectively represent the positions of the loudspeaker before and after sliding along the sliding device;

5. preferably, the signal processing unit 8 may be a computer, an oscilloscope or a spectrometer;

6. in an improved mode, an optical attenuator 218 is additionally arranged between the multi-longitudinal-mode laser and the beam splitter, the optical attenuator 218 is used for adjusting the light intensity of feedback light received by the laser, and the feedback light is prevented from being too strong or exceeding a laser damage threshold, so that the accuracy of a measurement result is further ensured, and the optical attenuator can be a displacement type attenuator, an attenuation sheet type attenuator or other types of optical attenuators;

7. in the improved mode, the multi-longitudinal-mode laser 1 adopts a semiconductor laser, and integrates a photodiode in the semiconductor laser by utilizing the characteristics of the semiconductor laser to realize the function of the photoelectric detector, thereby simplifying the optical path of the whole device and removing a beam splitter and the photoelectric detector.

In summary, the invention has the following advantages:

1. the sensing unit of the measuring device is a passive optical sensor, and power supply is not needed;

2. the test device has smaller volume and lower cost;

3. non-contact real-time high-precision measurement can be realized;

4. the optical path of the measuring device is a single optical path, the measuring device is small in environmental interference, simple in structure and convenient to adjust the optical path;

5. the sensitivity and the resolution of angle measurement can be adjusted by designing and selecting different external cavity measuring tools through parameters of the sensing unit;

6. the optical path structure of the sensing unit is selected variously, and the sensing unit with corresponding characteristics can be selected according to specific requirements.

It should be understood that the detailed description of the invention is merely illustrative of the invention and is not intended to limit the invention to the specific embodiments described. It will be appreciated by those skilled in the art that the present invention may be modified or substituted equally as well to achieve the same technical result; as long as the use requirements are met, the method is within the protection scope of the invention.