A millimeter wave-based micro-level high-precision absolute ranging system and method

Abstract

The application provides a millimeter wave-based micro-level high-precision absolute distance measuring system and method, which comprises the following steps: preparing and setting parameters of a phase self-adaptive stable phase system (PASS); testing the initial length of a free space to be measured by using a laser tracker; setting a sweep frequency output for the PASS frequency synthesizer and respectively measuring the phases corresponding to each frequency point under the condition of containing or not containing the free space; and calculating the absolute distance of the free space by using a sweep frequency plus point frequency high-precision absolute distance measuring algorithm. The application can break through the limitation of the relative distance measurement of the PASS, achieve the goal of dynamically measuring the length of the free space, and the measurement precision reaches 5 um, so that the problem that the dynamic distance measurement range of the PASS is limited is solved well, and the measurement precision of the PASS is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of submillimeter wave radio astronomy telescopes, and particularly relates to a millimeter wave-based micron-level high-precision absolute ranging system and method. BACKGROUND

[0002] Single-aperture millimeter / submillimeter wave radio telescopes are of great significance for astronomical observation. However, due to the limitations of existing technologies, the apertures of single-aperture submillimeter wave radio telescopes at home and abroad are relatively small, and the observation sensitivity and resolution are relatively low, which cannot meet the needs of large-area sky surveys. By increasing the aperture of the telescope to improve its observation performance, the detection of the main reflector surface shape precision becomes increasingly important. However, the traditional detection methods such as total station measurement, laser tracker measurement, digital photogrammetry, and holographic measurement have high measurement accuracy but are complex to operate and cannot be measured in real time, which cannot meet the requirements of high-precision and real-time measurement. The present inventors first proposed a phase adaptive stabilization system (PASS) in Chinese Patent Application CN114784509A. The system transmits a fixed frequency, interferes two signals of a radio frequency measurement and a reference, calculates the phase change of the radio frequency measurement through digital correlation, and obtains the displacement change. This method can not only measure the change of the main reflector surface shape of the antenna caused by disturbance in real time, but also has high measurement accuracy. Since the system is based on relative phase measurement, the measurement phase change is not more than 2π, and the displacement change is not more than 1 wavelength of the signal, thereby limiting the dynamic measurement range of the system. SUMMARY

[0003] The application provides a millimeter wave-based micron-level high-precision absolute ranging system and method to overcome the deficiencies in the prior art.

[0004] To achieve the above object, the application adopts the following technical solutions:

[0005] A millimeter-wave-based micron-level high-precision absolute ranging system, characterized by comprising: a phase adaptive stabilization system PASS, a laser tracker, a displacement platform, and a displacement controller; the PASS comprises a transmitting antenna, a receiving antenna, a radio frequency synthesizer, a local oscillator frequency synthesizer, a mixer A, a mixer B, a phase measurement subsystem, and a host computer; the host computer controls the movement of the displacement platform through the displacement controller, and the displacement platform is equipped with a transmitting antenna; the laser tracker is equipped with two target balls, which are respectively fixed above the transmitting antenna and the receiving antenna, and the laser tracker is equipped with ... phase adaptive stabilization system PASS, a phase adaptive stabilization system PASS The instrument is used to measure the spatial distance between two target balls; the host computer controls the radio frequency synthesizer and the local oscillator frequency synthesizer to output sweep frequency signals; the sweep frequency signal output by the radio frequency synthesizer is divided into two paths by a coupler, one path is transmitted to the transmitting antenna, and the other path is transmitted to mixer A; the sweep frequency signal output by the local oscillator frequency synthesizer is divided into two paths by a coupler, one path is transmitted to mixer A, and the other path is transmitted to mixer B; the signal received by the receiving antenna is transmitted to mixer B through a low noise amplifier; the phase measurement subsystem measures the output signals of mixer A and mixer B, and transmits the measured data to the host computer.

[0006] To optimize the above technical solutions, specific measures taken also include:

[0007] Furthermore, the phase measurement subsystem includes an amplifier, an attenuator, a filter and a digital correlator connected in sequence, and is used to perform multi-frequency phase testing.

[0008] Accordingly, the present invention proposes an absolute ranging method using the above-mentioned millimeter-wave-based micron-level high-precision absolute ranging system, which is characterized by comprising the following steps:

[0009] S1: Open the PASS software and hardware, and control the hardware initialization through the host computer software settings;

[0010] S2: Open the laser tracker's hardware and software and initialize it. Use the laser tracker to measure the distance between the two target balls, which is used to represent the initial length L of the free space to be measured. check ;

[0011] S3: Use the host computer to control the RF frequency synthesizer and the local oscillator frequency synthesizer to output signals in a sweep mode. Use the phase measurement subsystem to complete the phase test of each point frequency signal and save the data.

[0012] S4: Calculate the absolute distance L of the free space to be measured HP ;

[0013] S5: Set the absolute distance L between the free space to be measured HP With the initial length L check Make the difference and get the fixed correction value ΔL;

[0014] S6: During the real-time measurement process, the fixed correction amount ΔL is subtracted from the real-time measured absolute distance in free space, thereby obtaining the real-time absolute distance in free space.

[0015] Furthermore, in step S2, the laser tracker is used to track the center coordinates A(x A ,y A , z A ) and B(x B ,y B , z B ) Calculate the spatial distance between the two target balls. The calculation formula is as follows:

[0016]

[0017] Furthermore, in step S3, the host computer controls the sweep frequency output frequency of the RF frequency synthesizer to be f RF_i , i∈(1, 2, ..., n), controls the sweep frequency output frequency of the local oscillator frequency synthesizer to be f LO_i , i∈(1, 2, ..., n), the phase measurement subsystem measures the relative phase φ i , i∈(1, 2, …, n), where n represents the number of frequency points; among them, the signal path from the RF frequency synthesizer, through the transmitting antenna, free space, receiving antenna, and mixer B, to the phase measurement subsystem is the RF path, and the signal path through mixer A to the phase measurement subsystem is the correlation path.

[0018] Furthermore, the absolute distance L of the free space to be measured is obtained by measuring and calculating HP , specifically including the following two steps:

[0019] Step 1: Measure the RF path length and reference path length with and without free space, and calculate the free space length L accordingly. fs ;

[0020] Step 2: According to L fs Calculate the number of whole wavelengths N of each frequency signal transmitted in free space i and the whole wavelength length N i λ i ; Obtain the relative phase Δλ corresponding to each frequency point in the frequency sweep through the phase measurement subsystem i According to N i λ i and Δλ i Combined with the average method, the absolute distance L in free space is calculated HP .

[0021] Furthermore, the free space length L fs The specific calculation process is as follows:

[0022] The length of the radio frequency path relative to the reference path length L1-L2 under the condition of containing free space is calculated as follows:

[0023]

[0024] wherein L1 and L2 represent the length of the radio frequency path and the length of the reference path respectively, Δφ 12 represents the phase difference corresponding to different frequencies of the radio frequency path relative to the reference path, c represents the propagation speed of light in a vacuum medium, and n eff represents the effective refractive index;

[0025] The transmitting antenna and the receiving antenna are directly connected through a connector, and the length of the radio frequency path becomes L3;

[0026] The length of the radio frequency path relative to the reference path length L3-L2 under the condition of not containing free space is calculated as follows:

[0027]

[0028] wherein Δφ' 32_i represents the unwound phase difference corresponding to different frequencies of the radio frequency path relative to the reference path;

[0029] The difference between L1-L2 and L3-L2 is obtained as the length of free space L fs :

[0030] L fs =(L1-L2)-(L3-L2).

[0031] Further, the specific calculation process of the absolute distance L HP of free space is as follows:

[0032] According to the length of free space L fs , the whole wavelength number N i of the signal at each frequency transmitted in the free space is calculated as follows:

[0033]

[0034] wherein λ i represents the wavelength;

[0035] Under the condition of each frequency, the distance L HP_i of the signal at each frequency passing through the free space is calculated as follows:

[0036] L HP_i =N i λ i +Δλ i , i=1, 2, …, n;

[0037] Through L HP_iThe absolute distance L of the free space is calculated in an average way HP is:

[0038]

[0039] The beneficial effects of the present application are: on the basis of the point frequency PASS, the present application proposes to measure the length of the free space transmission between the entire transmitting antenna and the receiving antenna in a sweeping frequency way, which greatly expands the dynamic measurement range of the original point frequency PASS; in addition, the measurement accuracy can be improved and the accidental error that may exist in the point frequency PASS can be avoided by calculating the average displacement through the multi-frequency point phase. The present application breaks through the limitation that the measurement range of the original point frequency PASS does not exceed one signal wavelength, and maintains the measurement accuracy of the original point frequency PASS, which provides effective support for the further practicalization of the PASS. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 is a flow chart of a millimeter wave-based micron-level high-precision absolute ranging method of the present application;

[0041] Figure 2 is a relationship diagram between the distance between the target balls measured by the laser tracker and the platform displacement under the condition of 8-step displacement of the high-precision displacement platform and single-step 5mm;

[0042] Figure 3 is a block diagram of the sweeping frequency PASS absolute ranging system;

[0043] Figure 4 is a relationship diagram between the sweeping frequency PASS absolute ranging and the platform displacement under the condition of 8-step displacement of the high-precision displacement platform and single-step 5mm;

[0044] Figure 5 is a comparison diagram of the two ranging methods at a certain period after the sweeping frequency PASS is corrected. DETAILED DESCRIPTION

[0045] The present application will now be further described in detail in conjunction with the accompanying drawings.

[0046] Example 1

[0047] As Figure 3As shown, the application proposes a millimeter wave-based micron-level high-precision absolute ranging system, which comprises a phase adaptive stable phase system PASS, a laser tracker, a displacement platform and a displacement controller; the PASS comprises a transmitting antenna, a receiving antenna, a radio frequency synthesizer, a local oscillator frequency synthesizer, a mixer A, a mixer B, a phase measurement subsystem and an upper computer, the upper computer controls the movement of the displacement platform through the displacement controller, and the transmitting antenna is installed on the displacement platform; the laser tracker is provided with two target balls A and B, the two target balls are respectively fixed above the transmitting antenna and the receiving antenna, and the laser tracker is used for measuring the spatial distance of the two target balls; the upper computer controls the radio frequency synthesizer and the local oscillator frequency synthesizer to output a sweep frequency signal; the sweep frequency signal output by the radio frequency synthesizer is divided into two paths by a coupler, one path is transmitted to the transmitting antenna, and the other path is transmitted to the mixer A; the sweep frequency signal output by the local oscillator frequency synthesizer is divided into two paths by a coupler, one path is transmitted to the mixer A, and the other path is transmitted to the mixer B; the signal received by the receiving antenna is transmitted to the mixer B through a low-noise amplifier; the phase measurement subsystem measures the output signals of the mixer A and the mixer B, and transmits the measured data to the upper computer.

[0048] In this embodiment, the phase measurement subsystem comprises an amplifier, an attenuator, a filter and a digital correlator connected in sequence, and is used for performing multi-frequency point phase testing.

[0049] Embodiment two

[0050] As Figure 1 shown, the application proposes a millimeter wave-based micron-level high-precision absolute ranging method, which is based on the millimeter wave-based micron-level high-precision absolute ranging system proposed in embodiment one and is executed, and the specific process comprises:

[0051] S1: open the software and hardware of the PASS, and set and control the hardware module initialization through the upper computer software;

[0052] S2: fix the laser tracker target balls above the transmitting antenna and the receiving antenna, then open the software and hardware of the laser tracker and complete the initialization, and measure the spatial distance L of the two target balls check , so as to represent the initial length of the free space to be measured;

[0053] S3: use the upper computer of the PASS to control the two frequency synthesizers to output in the sweep frequency mode, then complete the phase testing of each point frequency signal through the PASS phase measurement subsystem and save the data;

[0054] S4: calculate the absolute distance L HP of the free space to be measured through the sweep frequency plus point frequency high-precision absolute ranging algorithm

[0055] S5: compare L HP calculated in S4 with L checkThe difference is obtained, and a fixed correction amount ΔL is obtained;

[0056] S6: In the absolute distance real-time dynamic measurement process, the free space absolute distance obtained by real-time measurement is subtracted by ΔL, so as to obtain the free space real-time absolute distance.

[0057] In this embodiment, after S1 is completed, first, the high-precision displacement platform (Beijing Zolix Zolix MC600, displacement accuracy 1-2um) on the optical platform is controlled by the host computer program to move unidirectionally for 8 steps, each step being 5mm, and the laser tracker is used to measure once after starting and after each step is completed, so as to obtain the relationship data between the laser tracker and the high-precision platform displacement, and a relationship diagram is drawn as shown in Figure 2 The laser tracker measures the spatial distance L check between the two target balls, and according to the coordinates A(x A , y A , z A ) and B(x B , y B , z B ), the expression is calculated as formula (1):

[0058]

[0059] Figure 3 The block diagram of the frequency sweeping PASS absolute distance measurement system is shown in the figure. In S3, the PASS host computer outputs instructions to control one of the radio frequency synthesizers to output a sweeping signal with a center frequency of 24GHz, a frequency width of 100MHz, a frequency point number of 17, and a frequency point interval of 6.25MHz, and the other radio frequency synthesizer outputs a sweeping signal with a center frequency of 24.03GHz, a frequency width of 100MHz, a frequency point number of 17, and a frequency point interval of 6.25MHz, and the frequencies output by the two synthesizers are always different by 30MHz. In the calibration experiment, the laser tracker distance measurement experiment is carried out synchronously, and the high-precision displacement platform of the optical platform is moved 8 times, each time by 5mm, and the frequency sweeping PASS is used to measure once after starting and after each step is completed, and the specific algorithm of each step is as follows:

[0060] The PASS host computer controls the radio frequency (RF) sweeping output frequency f RF_i , i∈(1, 2, …, 17), and the local oscillator (LO) sweeping output frequency f LO_i , i∈(1, 2, …, 17), and the PASS digital correlator obtains the relative phase φ i , i∈(1, 2, …, 17), and finally formula (2) is obtained by derivation:

[0061]

[0062] where L represents the relative length of the radio frequency path and the reference path, Δφ represents the difference of the unwrapped phase at the start and end of the sweep, Δf is 100 MHz, n eff represents the effective refractive index; c represents the speed of light in a vacuum medium; wherein the radio frequency path is from the radio frequency synthesizer through the through port of the directional coupler, through the transmitting antenna, the free space to the receiving antenna, into the receiving system and mixed with the local oscillator signal, and the intermediate frequency signal is output to the digital correlator; the reference path is from the radio frequency synthesizer through the coupled port of the directional coupler, directly mixed with the local oscillator signal of the other path of the power divider, and the intermediate frequency signal is output to the digital correlator.

[0063] Since the digital correlator measures the relative phase within 2π, the absolute phase must be obtained through the phase unwrapping algorithm here. The phase unwrapping algorithm is written as follows through MATLAB:

[0064]

[0065]

[0066] The specific PASS sweep measurement process is divided into two steps:

[0067] First, the lengths of the radio frequency path and the reference path under the conditions of containing and not containing the free space are measured respectively, and the length of the free space part is roughly obtained as L fs .

[0068] Then according to formula (2), the relationship between the different frequencies of the radio frequency path and the reference path and their corresponding phases (not unwrapped) is shown in formulas (3) and (4):

[0069]

[0070] Then through the phase unwrapping algorithm, the difference Δφ 12_i between the different frequencies of the radio frequency path relative to the reference path and their corresponding unwrapped phase under the condition of containing the free space is shown in formula (5):

[0071]

[0072] Further, the length L1-L2 of the radio frequency path relative to the reference path under the condition of containing the free space is formula (6):

[0073]

[0074] In a short time, the two antennas are directly connected through the connector, and the phase measurement experiment without containing the free space is carried out, the length of the radio frequency path becomes L3, and the radio frequency path and its corresponding phase relationship is shown in formula (7), and the reference path does not change.

[0075]

[0076] Under this condition, the unfolded phase Δφ′ of each frequency point is obtained 32_i As shown in formula (8):

[0077]

[0078] Furthermore, under the condition of no free space (direct connection), the length of the radio frequency path relative to the reference path L3-L2 is as shown in formula (9):

[0079]

[0080] At this time, if we directly make the difference between equations (6) and (9) and only use the absolute distance measurement method, we can get the free space length L fs :

[0081] L fs =(L1-L2)-(L3-L2) (10)

[0082] The second step needs to be divided into three steps. The first step is to calculate the number of whole wavelengths N contained in free space under each frequency signal. i and the whole wavelength length N i λ i The second step is to obtain the relative phase Δλ corresponding to each frequency point in the frequency sweep through the digital correlator. i ; The third step is to calculate the high-precision absolute displacement L by averaging HP The details are as follows:

[0083] According to the free space length L fs , calculate the number of whole wavelengths N in which each frequency signal is transmitted i :

[0084]

[0085] Then, under various frequency conditions, the distance L through free space is calculated. HP _i:

[0086] L HP_i =N i λ i +Δλ i , i=1,2,…,n (12)

[0087] Then through L HP_i Averaging method to obtain high-precision absolute measurement results L HP , that is, the absolute distance in free space, can effectively avoid accidental errors at individual points, thereby improving measurement accuracy.

[0088]

[0089] Through the above algorithm, the single-step free space length can be obtained, and the dynamic measurement of 8 steps can obtain the relationship data between the frequency-sweeping PASS absolute ranging and the high-precision platform displacement, and the relationship diagram is shown in Figure 4

[0090] In S6, the results measured by the laser tracker and the frequency-sweeping PASS absolute ranging in the same period are compared, and then the result of the frequency-sweeping PASS absolute ranging is subtracted from the result of the laser tracker ranging, so as to obtain the fixed correction amount of the frequency-sweeping PASS absolute ranging. In the formal measurement, the real-time frequency-sweeping PASS absolute ranging result is corrected to obtain the real-time micrometer-level high-precision dynamic measurement result.

[0091] As shown in Figure 5 After the frequency-sweeping PASS absolute ranging result is corrected, in the real-time measurement, the result detected by the laser tracker in the period is compared, it can be directly obtained that the linear fitting curves of the two are close to coincidence; from the comparison of the linear fitting intercepts of the two, the difference is about tens of microns, and from the fitting slopes of the two, when the free space length changes by 1 mm, the difference between the two ranging methods is less than 1 um.

[0092] The above is only the preferred embodiment of the present application, and the protection scope of the present application is not limited to the above-mentioned embodiments only, and any technical solution falling within the idea of the present application belongs to the protection scope of the present application. It should be noted that, for ordinary skilled in the art, some improvements and decorations without departing from the principles of the present application should be considered as the protection scope of the present application.​

Claims

1. A millimeter-wave-based micro-scale high-precision absolute ranging system, characterized in that, Comprise: Phase adaptive stable phase system PASS, laser tracker, displacement platform and displacement controller; the PASS comprises a transmitting antenna, a receiving antenna, a radio frequency synthesizer, a local oscillator frequency synthesizer, a mixer A, a mixer B, a phase measurement subsystem and a host computer, the host computer controls the movement of the displacement platform through the displacement controller, the transmitting antenna is installed on the displacement platform; the laser tracker is configured with two target balls, the two target balls are respectively fixed above the transmitting antenna and the receiving antenna, and the laser tracker is used for measuring the spatial distance of the two target balls; the host computer controls the radio frequency synthesizer and the local oscillator frequency synthesizer to output sweep signals; the sweep signals output by the radio frequency synthesizer are divided into two paths by a coupler, one path is transmitted to the transmitting antenna, and the other path is transmitted to the mixer A; the sweep signals output by the local oscillator frequency synthesizer are divided into two paths by a coupler, one path is transmitted to the mixer A, and the other path is transmitted to the mixer B; the signals received by the receiving antenna are transmitted to the mixer B through a low-noise amplifier; the phase measurement subsystem measures the output signals of the mixer A and the mixer B, and transmits the measured data to the host computer.

2. The millimeter-wave-based micro-scale high-precision absolute ranging system of claim 1, wherein: The phase measurement subsystem comprises an amplifier, an attenuator, a filter and a digital correlator connected in sequence, and is used for multi-frequency point phase test.

3. An absolute distance measuring method using the millimeter-wave-based micro-order high-precision absolute distance measuring system according to claim 1 or 2, characterized by, Comprise the following steps: S1: open the software and hardware of the PASS, and set the hardware initialization through the host computer software; S2: open the software and hardware of the laser tracker and initialize, measure the spatial distance of two target balls by the laser tracker, which is used to represent the initial length L of the free space to be measured check ; S3: use the host computer to control the radio frequency synthesizer and the local oscillator frequency synthesizer to output signals in sweep mode, complete the phase test of each point frequency signal through the phase measurement subsystem and save the data; S4: Calculate the absolute distance L of the free space to be measured HP ; S5: the absolute distance L of the free space to be measured is calculated according to the formula L = L0 + ΔL HP and the initial length L check is subtracted to obtain the fixed correction ΔL; S6: in the real-time measurement process, subtract the fixed correction amount ΔL from the free space absolute distance obtained by real-time measurement, so as to obtain the real-time absolute distance of free space.

4. The method of absolute ranging of claim 3, wherein: In step S2, the laser tracker calculates the spatial distance of the two target spheres according to the sphere center coordinates A(x A , y A , z A ) and B(x B , y B , z B ) of the two target spheres, and the calculation formula is as follows:

5. The method of absolute ranging of claim 3, wherein: In step S3, the host computer controls the sweep output frequency of the radio frequency synthesizer to be f RF_i , i∈(1, 2, …, n), controls the sweep output frequency of the local oscillator synthesizer to be f LO_i , i∈(1, 2, …, n), and the phase measurement subsystem measures the relative phase φ i , i∈(1, 2, …, n), n represents the number of frequency points; wherein, from the radio frequency synthesizer, through the transmitting antenna, the free space, the receiving antenna, the mixer B, the output signal to the phase measurement subsystem is the radio frequency path, and the output signal to the phase measurement subsystem through the mixer A is the correlation path.

6. The method of absolute ranging of claim 5, wherein: The measurement and calculation get the absolute distance L of the free space to be measured HP , in particular Comprise the following two steps: First step: measure the radio frequency path length and the reference path length in the condition of containing free space and in the condition of not containing free space respectively, and calculate the free space length L according to the measurement results fs ; Second step: according to L fs Calculate the whole wavelength number N of each frequency signal in free space i And the whole wavelength length N i λ i ; Obtain the corresponding relative phase Δλ of each frequency point in the sweep frequency by the phase measurement system i ; According to N i λ i And Δλ i , and combined with the average method, the absolute distance L of free space is calculated HP .

7. The method of absolute ranging of claim 6, wherein: The free space length L fs The specific calculation process is as follows: Calculate the length L1-L2 of the radio frequency path relative to the reference path under the condition of containing free space: wherein L1 and L2 represent the radio frequency path length and the reference path length, respectively, Δφ 12_i represents the phase difference corresponding to the different frequencies of the radio frequency path with respect to the reference path, c represents the propagation speed of light in a vacuum medium, n eff represents the effective refractive index; The transmitting antenna and the receiving antenna are directly connected through the connector, and the length of the radio frequency path becomes L3; Calculate the length L3-L2 of the radio frequency path relative to the reference path under the condition of not containing free space: where Δφ' represents the unwrapped phase difference corresponding to the difference in frequency between the radio frequency path and the reference path; and 32_i where Δφ' represents the unwrapped phase difference corresponding to the difference in frequency between the radio frequency path and the reference path; and L1 - L2 and L3 - L2 to obtain the free space length L fs : L fs = (L1 - L2) - (L3 - L2).

8. The method of absolute ranging of claim 6, wherein: The free space absolute distance L HP The specific calculation process is as follows: According to the free space length L fs , the whole wavelength number N i of each frequency signal transmitted in the free space is calculated as: where λ i represents the wavelength; Under each frequency condition, the distance L of each frequency signal through the free space is calculated HP_i : L HP_i = N i λ i + Δλ i , i = 1, 2,..., n; By means of the L HP_i The absolute distance L HP is calculated in an average manner:

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