US-20260126286-A1 - LASER TRACKING INTERFEROMETRIC SPATIAL COORDINATE MEASUREMENT SYSTEM AND METHOD BASED ON DUAL ELECTRO-OPTICAL FREQUENCY COMB

US20260126286A1US 20260126286 A1US20260126286 A1US 20260126286A1US-20260126286-A1

Abstract

The disclosure discloses a laser tracking interferometric spatial coordinate measurement system and a method thereof based on dual electro-optical frequency comb. Multi-target mirrors are identified, guiding a rotating mirror to direct a laser beam to each target. A tracking error of the laser beam deviating from the target center is obtained for closed-loop tracking control. A single-frequency laser traceable to gas absorption peaks is outputted. By turning the electro-optic phase modulation drive signal on or off, either dual electro-optic frequency comb or dual-frequency continuous-wave laser is outputted. Under tracking mode, the absolute distance and relative displacement of the target mirror are measured using the two light sources respectively, obtaining the real-time distance between the target mirror and an origin through data fusion. The azimuth and elevation angles are acquired in real time. Tracking control and coordinate calculation are performed, obtaining 3 D spatial coordinates of all target mirrors.

Inventors

Benyong Chen
Liping Yan
Jiandong Xie
Yingtian LOU

Assignees

ZHEJIANG SCI-TECH UNIVERSITY

Dates

Publication Date: 20260507
Application Date: 20251229
Priority Date: 20240521

Claims (10)

1 . A laser tracking interferometric spatial coordinate measurement system based on a dual electro-optical frequency comb, wherein: the laser tracking interferometric spatial coordinate measurement system is divided into three parts comprising a precision optical tracking unit, a ranging unit based on the dual electro-optical frequency comb, and an electrical control unit; a part of the precision optical tracking unit is mounted on a frame body, and another part is mounted on an object under test or a space under test, wherein the ranging unit is mounted within the frame body, the electrical control unit is electrically connected to the precision optical tracking unit and the ranging unit respectively, and the electrical control unit controls the ranging unit based on the dual electro-optical frequency comb to emit a dual electro-optical frequency comb beam that is reflected and adjusted by the precision optical tracking unit to be incident on the object under test or the space under test and then received to perform spatial coordinate measurement of the object under test or the space under test.
2 . The laser tracking interferometric spatial coordinate measurement system based on the dual electro-optical frequency comb according to claim 1 , wherein: the precision optical tracking unit mainly comprises a target mirror assembly, a rotating mirror, a pitch torque motor, a vision module, a pitch angle measurement module, an azimuth torque motor, and an azimuth angle measurement module; the target mirror assembly is arranged on the object under test or in the space under test; the azimuth torque motor is mounted on an upper end of the frame body, a rotating end of the azimuth torque motor has a rotating mirror shaft and a vision shaft parallel to each other horizontally mounted through a bracket, and the rotating end of the azimuth torque motor is provided with the azimuth angle measurement module for detecting a rotation angle; an end of the rotating mirror shaft is coaxially and fixedly connected to a rotating end of the pitch torque motor, another end of the rotating mirror shaft is connected to the pitch angle measurement module for measuring the rotation angle of the rotating mirror shaft, and the rotating mirror is fixedly mounted on the rotating mirror shaft; the vision shaft is rotatably mounted on the bracket through a gear assembly, and the vision module is fixedly mounted on the vision shaft.
3 . The laser tracking interferometric spatial coordinate measurement system based on the dual electro-optical frequency comb according to claim 1 , wherein: the ranging unit based on the dual electro-optical frequency comb comprises a beam adjustment module, a laser tracking interferometric ranging module, a light source modulation module, and a light source module arranged sequentially from a bottom to a top; the light source module outputs a single-frequency laser traceable to a gas absorption peak, the single-frequency laser is transmitted through a polarization-maintaining fiber to the light source modulation module for electro-optical phase modulation to generate the dual electro-optical frequency comb, the dual electro-optical frequency comb is transmitted to the laser tracking interferometric ranging module, the laser tracking interferometric ranging module outputs a measurement light transmitted to the beam adjustment module, the beam adjustment module expands and collimates the measurement light and then performs translation and deflection control adjustment to make the measurement light incident to a center of a rotating mirror, wherein after being reflected by the rotating mirror, the measurement light is incident on the target mirror assembly of the object under test or the space under test, and returns to the laser tracking interferometric ranging module after being reflected by the target mirror assembly.
4 . The laser tracking interferometric spatial coordinate measurement system based on the dual electro-optical frequency comb according to claim 1 , wherein: a pitch torque motor, a vision module, a pitch angle measurement module, an azimuth torque motor and an azimuth angle measurement module within the precision optical tracking unit are electrically connected through a wire and a coaxial conductive ring disposed at an upper end of the frame body.
5 . The laser tracking interferometric spatial coordinate measurement system based on the dual electro-optical frequency comb according to claim 1 , wherein: the electrical control unit mainly comprises a power supply module, a tracking control and signal processing module and a computer, wherein the tracking control and signal processing module and the computer are electrically connected, the power supply module and the tracking control and signal processing module are connected for power supply, the tracking control and signal processing module is electrically connected to the precision optical tracking unit and the ranging unit respectively; and the laser tracking interferometric spatial coordinate measurement system further comprises an environmental monitoring sensor, the environmental monitoring sensor is electrically connected to the tracking control and signal processing module of the electrical control unit, the environmental monitoring sensor is for measuring a temperature parameter, a humidity parameter and an air pressure parameter of air and transmitting the same wirelessly to the tracking control and signal processing module.
6 . The laser tracking interferometric spatial coordinate measurement system based on the dual electro-optical frequency comb according to claim 1 , wherein: a tracking control and signal processing module of the electrical control unit processes and outputs a closed-loop control signal according to a target mirror information in an image obtained by a vision module and a tracking error signal obtained by a laser tracking interferometric ranging module, thereby controlling an azimuth torque motor and a pitch torque motor to jointly rotate a rotating mirror to track a target mirror; simultaneously, an azimuth angle measurement module and a pitch angle measurement module acquire an angle information of a pitch angle and an azimuth angle of the target mirror in real-time under a tracking condition, wherein combining with a distance information obtained by the laser tracking interferometric ranging module, synchronous matching of the angle information and the distance information is performed, and after processing by a computer, a three-dimensional coordinate of each target mirror in the target mirror assembly is obtained.
7 . The laser tracking interferometric spatial coordinate measurement system based on the dual electro-optical frequency comb according to claim 1 , wherein: the laser tracking interferometric ranging module comprises a laser diode, a fiber polarization-maintaining combiner, a first collimator, a first polarizing beamsplitter, a reference corner cube prism, a filter, a first quarter-wave plate, a second quarter-wave plate, a second collimator, a color separator, a second polarizing beamsplitter, a first photodetector, a second photodetector, a two-dimensional position detector, and a right-angle mirror mounted in a shielding enclosure; the ranging unit emits a measurement light from the dual electro-optical frequency comb and incidents to the fiber polarization-maintaining combiner together with an indication light emitted by the laser diode to for light combination, forming a first combined beam, and the first combined beam is then expanded and collimated by the first collimator and then incident to the first polarizing beamsplitter to undergo a first transmission and a first reflection; the first combined beam after the first reflection by the first polarizing beamsplitter sequentially passes through the first quarter-wave plate and the filter and is reflected by the reference corner cube prism, then returns along an original path in reverse to the first polarizing beamsplitter to undergo a second transmission; the first combined beam after the first transmission by the first polarizing beamsplitter sequentially passes through the second quarter-wave plate, is reflected by the right-angle mirror, then exits through a window plate on the shielding enclosure to a beam adjustment module, wherein after being adjusted by the beam adjustment module, the first combined beam is incident to the target mirror assembly, and after being reflected by the target mirror assembly, the first combined beam returns along the original path in reverse to the first polarizing beamsplitter to undergo a second reflection; wherein light beams retroreflected back to the first polarizing beamsplitter and undergo the second reflection and the second transmission are combined to form a second combined beam, the second combined beam is then incident on the color separator where transmission and reflection occur, a beam reflected by the color separator is incident on the two-dimensional position detector and received to obtain a tracking error signal, a beam transmitted by the color separator is then incident on the second polarizing beamsplitter where reflection and transmission occur respectively, a reference light from the dual electro-optical frequency comb emitted by the ranging unit undergoes beam expansion and collimation through the second collimator and is then incident on the second polarizing beamsplitter where reflection and transmission occur, a beam of the reference light reflected by the second polarizing beamsplitter and a beam of the second combined beam transmitted by the second polarizing beamsplitter are incident together on the first photodetector and received to obtain a reference interference signal, the beam of the reference light transmitted by the second polarizing beamsplitter and the beam of the second combined beam reflected by the second polarizing beamsplitter are incident together on the second photodetector and received to obtain a measurement interference signal.
8 . The laser tracking interferometric spatial coordinate measurement system based on the dual electro-optical frequency comb according to claim 1 , wherein: a tracking control and signal processing module comprises an image processing module, a tracking error signal preprocessing module, an angle decoding module, a tracking control module, a motor driver, a synchronization module and a signal processing module, and the signal processing module comprises an absolute distance measurement signal processing module, an air refractive index calculation module, a relative displacement measurement signal processing module and a distance fusion module; input terminals of the image processing module, the tracking error signal preprocessing module and the angle decoding module are electrically connected to a vision module, a two-dimensional position detector, and an azimuth angle measurement module respectively, input terminals of both the absolute distance measurement signal processing module and the relative displacement measurement signal processing module are electrically connected to a first photodetector and a second photodetector, an input terminal of the air refractive index calculation module is electrically connected to an environmental monitoring sensor, and an output terminal of the air refractive index calculation module is also connected to the absolute distance measurement signal processing module and the relative displacement measurement signal processing module respectively; output terminals of the absolute distance measurement signal processing module and the relative displacement measurement signal processing module are connected to a distance fusion module, output terminals of the image processing module, the tracking error signal preprocessing module, the angle decoding module and the distance fusion module are all simultaneously connected to the tracking control module, and an output terminal of the tracking control module is connected to an azimuth torque motor and a pitch torque motor via the motor driver; the output terminals of the angle decoding module and the distance fusion module are both connected to the synchronization module, and an output terminal of the synchronization module is connected to a computer.
9 . A laser tracking interferometric spatial coordinate measurement and control method based on a dual electro-optical frequency comb for the laser tracking interferometric spatial coordinate measurement system according to claim 1 , comprising: 1 ) a light source module outputting a single-frequency laser traceable to a gas absorption peak, wherein the single-frequency laser is transmitted through a polarization-maintaining fiber to a light source modulation module for electro-optical phase modulation to generate the dual electro-optical frequency comb, the dual electro-optical frequency comb is transmitted to a laser tracking interferometric ranging module, the laser tracking interferometric ranging module outputs a measurement light transmitted to a beam adjustment module, the beam adjustment module expands and collimates the measurement light and then performs translation and deflection control adjustment to make the measurement light incident to a center of a rotating mirror, wherein after being reflected by the rotating mirror, the measurement light is incident on the target mirror assembly of the object under test or the space under test, and returns to the laser tracking interferometric ranging module after being reflected by the target mirror assembly for real-time receipt of a tracking error signal, a reference interference signal and a measurement interference signal; 2 ) controlling a modulation of turning on and off of the light source modulation module, and then measuring and obtaining an absolute distance and a relative displacement through the laser tracking interferometric ranging module in an absolute ranging mode and a relative displacement mode respectively;meanwhile measuring air parameter signals through an environmental monitoring sensor, obtaining an angle measurement signal of a pitch angle and an azimuth angle of the rotating mirror in real time through a pitch angle measurement module and an azimuth angle measurement module, and obtaining an image frame of the target mirror assembly in real time through a vision module; 3 ) inputting the obtained tracking error signal, the reference interference signal, the measurement interference signal, the air parameter signals, the angle measurement signal, the image frame, the absolute distance and the relative displacement to a tracking control and signal processing module for processing, and controlling a rotation control of a pitch torque motor and an azimuth torque motor to further control a rotation of the rotating mirror, achieving closed-loop tracking of the target mirror assembly, while also converting a synchronized angle information and a distance information into a three-dimensional coordinate for display.
10 . The laser tracking interferometric spatial coordinate measurement and control method based on the dual electro-optical frequency comb according to claim 9 , wherein: in a step 3 ), in the tracking control and signal processing module, the air parameter signals, the reference interference signal, the measurement interference signal, and the angle measurement signal are transmitted to the tracking control and signal processing module for processing, wherein the angle measurement signal is transmitted to an angle decoding module for decoding to obtain the angle information, the reference interference signal and the measurement interference signal are transmitted to a signal processing module for processing and compensation using the air parameter signals to obtain the distance information, the tracking error signal is transmitted to a tracking error signal preprocessing module for processing a position deviation information between the measurement light spot and a center of a target mirror, and the image frame is transmitted to the image processing module for processing to obtain an identification information of all target mirrors; on one aspect, the identification information, the position deviation information, the angle information and the distance information of all target mirrors are transmitted to a tracking control module, processed through a closed-loop control algorithm to obtain a feedback control signal, and transmitted through a motor driver to the pitch torque motor and the azimuth torque motor to control the rotating mirror to rotate, thereby achieving closed-loop tracking of the target mirror; on another aspect, synchronization processing is performed by a synchronization module to eliminate a delay between the angle information and the distance information, and then the synchronized angle information and the distance information are transmitted to a computer for conversion to and display of a three-dimensional coordinate.

Description

CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation of international PCT application serial no. PCT/CN2025/087534, filed on April 7, 2025, which claims the priority benefit of China application no. 202410631580.8, filed on May 21, 2024. The entirety of each of the above–mentioned patent applications is hereby incorporated by reference herein and made a part of this specification. TECHNICAL FIELD The disclosure belongs to the field of laser tracking measurement technology, and more particularly to a laser tracking interferometric spatial coordinate measurement system and a method thereof based on a dual electro-optical frequency comb. Related Art Laser tracking interferometric measurement technology is widely applied in fields such as large-scale high-end equipment assembly and industrial robot positioning accuracy calibration due to its advantages of large measurement range, high precision, and fast speed. Distance measurement is the core technology of laser tracking interferometric measurement. Existing laser tracking interferometric measurement methods typically adopt a combination of absolute distance measurement (ADM) and relative displacement measurement (RDM) for ranging measurement. The ADM method may obtain absolute distance and may resume measurement after beam interruption, but is only suitable for static measurement. The RDM method may achieve high-speed displacement measurement, but the measurement result is displacement increment, and beam interruption will cause measurement failure. The combined measurement approach combines the advantages of both measurement methods, but requires combining the measurement light of two measurement units into one laser beam before measurement. When mechanical components used to fix optical elements slowly deform over time, the combined light beam will bifurcate, thereby introducing measurement errors. On the other hand, the two ranging units have different distance reference zero points, which may introduce additional drift errors and increase system complexity and cost. Therefore, the prior art lacks the use of the same ranging unit to construct both ADM and RDM ranging modes to achieve high-precision absolute distance measurement, which is a technical problem that has not been solved in the field of laser tracking interferometric measurement. SUMMARY OF INVENTION To solve the problems existing in the background technology, the disclosure provides a laser tracking interferometric spatial coordinate measurement system and a method thereof based on a dual electro-optical frequency comb, adopting a single ranging module based on the dual electro-optical frequency comb to achieve both ADM and RDM ranging functions. The technical solution adopted by the disclosure to solve the technical problems is the following. I. A laser tracking interferometric spatial coordinate measurement system based on a dual electro-optical frequency comb, divided into three parts: a precision optical tracking unit, a ranging unit based on a dual electro-optical frequency comb, and an electrical control unit. A part of the precision optical tracking unit is mounted on the frame body, and another part is mounted on an object under test or a space under test. The ranging unit is mounted within the frame body. The electrical control unit is electrically connected to the precision optical tracking unit and the ranging unit respectively. The electrical control unit controls the ranging unit based on the dual electro-optical frequency comb to emit a dual electro-optical frequency comb beam that is reflected and adjusted by the precision optical tracking unit to be incident on the object under test or the space under test and then received to perform spatial coordinate measurement of the object under test or the space under test. The precision optical tracking unit mainly includes a target mirror assembly, a rotating mirror, a pitch torque motor, a vision module, a pitch angle measurement module, an azimuth torque motor, and an azimuth angle measurement module. The target mirror assembly is arranged on the object under test or in the space under test. The azimuth torque motor is mounted on an upper end of the frame body, and a horizontal and parallel rotating mirror shaft and vision shaft are mounted on a rotating end of the azimuth torque motor through a bracket, while the rotating end of the azimuth torque motor is provided with an azimuth angle measurement module for detecting a rotation angle. An end of the rotating mirror shaft is coaxially and fixedly connected to the rotating end of the pitch torque motor, another end of the rotating mirror shaft is connected to a pitch angle measurement module for measuring the rotation angle of the rotating mirror shaft, and a rotating mirror is fixedly mounted on the rotating mirror. The vision shaft is rotatably mounted on the bracket through a gear assembly, and a vision module is fixedly mounted on the vision shaft. The ranging