A high-precision tracking and ranging method for cooperative targets

Abstract

This invention discloses a high-precision tracking and ranging method for cooperative targets, belonging to the field of laser ranging. The method includes: initializing the measurement optical comb and sampling optical comb according to the expected distance and ranging accuracy requirements of the cooperative target, determining the scanning trajectory and scanning parameters for the initial scanning stage, the tracking scanning stage, and the target loss and recapture stage; driving the scanning mechanism to move to the target scanning point according to the received scanning tracking command, and maintaining a stationary position for a preset asynchronous sampling duration; completing the acquisition and calculation of the laser interference signal according to the dual-comb asynchronous sampling ranging optical path to obtain the target distance data corresponding to the current scanning point; determining whether the cooperative target has been successfully tracked based on whether stable and valid target distance data has been obtained, and continuously tracking the cooperative target based on the determination result. This invention can improve the tracking and ranging accuracy of cooperative targets.

Description

Technical Field

[0001] This invention relates to the field of laser imaging technology, and in particular to a high-precision tracking and ranging method for cooperative targets. Background Technology

[0002] Laser scanning tracking and ranging is playing an increasingly important role in various fields. In the space domain, it can be applied to distance measurement of cooperative targets and rendezvous and docking of space targets. According to different measurement principles, laser ranging can be divided into technical routes such as time-of-flight method, phase ranging method, and triangulation method. Among them, the time-of-flight method has been widely used in many scenarios such as rendezvous and docking of cooperative or non-cooperative targets in the aerospace field, navigation and obstacle avoidance for deep space exploration landing, as well as aerial refueling of military UAVs, civilian autonomous driving, and high-precision 3D mapping of cities.

[0003] In related technologies, traditional laser scanning tracking and ranging systems are limited by the fact that the response time of electronic devices is on the same order of magnitude as the flight time of light, resulting in low ranging accuracy. This makes them unsuitable for the application requirements of long-distance, dynamic target scanning and tracking in the aerospace field, and even more difficult to support ultra-high precision space measurement tasks.

[0004] Therefore, there is an urgent need for a high-precision tracking and ranging method for cooperative targets to solve the above-mentioned technical problems. Summary of the Invention

[0005] This invention provides a high-precision tracking and ranging method for cooperative targets, which can effectively improve the tracking and ranging accuracy of cooperative targets. The technical solution is as follows: On the one hand, a high-precision tracking and ranging method for cooperative targets is provided, the method comprising: Based on the expected distance and ranging accuracy requirements of the cooperative target, the measurement optical comb and sampling optical comb are initialized to determine the scanning trajectory and scanning parameters for the initial scanning stage, the tracking scanning stage, and the target loss and recapture stage. According to the received scanning tracking command, the scanning mechanism is driven to move to the target scanning point along the initial scanning trajectory and stays at the position for a preset asynchronous sampling time. The laser interference signal is acquired and calculated using the dual-comb asynchronous sampling ranging optical path to obtain the target distance data corresponding to the current scanning point. Based on whether stable and valid target distance data has been obtained, it is determined whether the cooperative target has been successfully tracked, and the cooperative target is continuously tracked based on the determination result.

[0006] On the other hand, a high-precision tracking and ranging system for cooperative targets is provided, the system comprising a parallel-arranged measurement optical frequency comb and a sampling optical frequency comb, and a scanning mechanism, wherein: The first beam splitter and the reference arm are arranged sequentially along the optical path propagation direction of the measurement optical frequency comb, and the reference arm is set in the refraction optical path of the first beam splitter. The second beam splitter and the asynchronous sampling circuit are sequentially arranged along the optical path propagation direction of the sampling optical frequency comb; The scanning mechanism is located in the transmission optical path of the first beam splitter, and the scanning mechanism driver, control circuit and asynchronous sampling circuit are electrically connected.

[0007] The technical solution provided by this invention can bring at least the following beneficial effects: Through the core method of dual-beam combing interferometry and asynchronous sampling calculation, the extremely short time of flight of light is linearly amplified tens of thousands of times, breaking through the accuracy bottleneck of the response bandwidth of traditional electronic devices. The ranging accuracy can reach the micrometer to nanometer level, achieving an order-of-magnitude improvement compared to traditional centimeter-level solutions. Through a rigid timing synchronization design of scanning and ranging, the core logic of strictly adhering to the point-station dwell time to complete the full-cycle ranging before stepping forward ensures accurate binding of angle and distance data, eliminating measurement failures caused by timing misalignment. Adopting a hierarchical tracking strategy of initial wide-range coarse scanning and narrow-range fine scanning after target loss, it balances target acquisition efficiency and recapture capability, is compatible with various scanning mechanisms and trajectories, and can be widely adapted to high-end precision measurement scenarios such as aerospace rendezvous and docking, significantly expanding the high-precision application boundaries of laser ranging. Attached Figure Description

[0008] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0009] Figure 1 This is a schematic diagram of a high-precision tracking and ranging method for cooperative targets provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of a fast-reflection mirror and ranging sampling provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the Lissajous curve trajectory scanning process provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of a tracking scan provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of a high-precision tracking and ranging system for cooperative targets provided in an embodiment of the present invention.

[0010] Figure descriptions: 1-Measuring optical frequency comb; 2-Sampling optical frequency comb; 3-First beam splitter; 4-Second beam splitter; 5-Reference arm; 6-Asynchronous sampling circuit; 7-Scanning mechanism; 8-Mechanism driver; 9-Control circuit. Detailed Implementation

[0011] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0012] Please refer to Figure 1 The present invention provides a high-precision tracking and ranging method for cooperative targets, the method comprising: Step 100: Initialize the measurement optical comb and sampling optical comb according to the expected distance and ranging accuracy requirements of the cooperative target, and determine the scanning trajectory and scanning parameters for the initial scanning stage, the tracking scanning stage, and the target loss and recapture stage; Step 102: Drive the scanning mechanism to move to the target scanning point according to the initial scanning trajectory based on the received scanning tracking command, and keep the position stationary for a preset asynchronous sampling time; Step 104: Complete the acquisition and calculation of the laser interference signal according to the dual-comb asynchronous sampling ranging optical path to obtain the target distance data corresponding to the current scanning point; Step 106: Determine whether the cooperative target has been successfully tracked based on whether stable and valid target distance data has been obtained, and continue to track the cooperative target based on the determination result.

[0013] In this embodiment of the invention, the core method of dual-beam combing interferometry and asynchronous sampling calculation linearly amplifies the extremely short time of flight of light by tens of thousands of times, breaking through the accuracy bottleneck of the response bandwidth of traditional electronic devices. The ranging accuracy can reach the micrometer to nanometer level, achieving an order-of-magnitude improvement compared to traditional centimeter-level solutions. Through a rigid timing synchronization design of scanning and ranging, the core logic of strictly adhering to the point-station dwell to complete the full cycle of ranging before stepping is strictly implemented, ensuring accurate binding of angle and distance data and eliminating measurement failures caused by timing misalignment. A hierarchical tracking strategy of initial wide-range coarse scanning and narrow-range fine scanning after target loss is adopted, which takes into account both target acquisition efficiency and recapture capability. It is compatible with various scanning mechanisms and trajectories and can be widely adapted to high-end precision measurement scenarios such as aerospace rendezvous and docking, greatly expanding the high-precision application boundaries of laser ranging.

[0014] For step 100, the measurement optical comb and sampling optical comb are initialized according to the expected distance and ranging accuracy requirements of the cooperative target, and the scanning trajectory and scanning parameters of the initial scanning stage, the tracking scanning stage and the target loss and recapture stage are determined.

[0015] In this embodiment of the invention, the initial scanning trajectory, the tracking scanning trajectory, and the recapture scanning trajectory all adopt any one of the following: a zigzag scanning, a Lissajous scanning, or a custom optical scanning trajectory.

[0016] The initial scanning phase uses a wide-range, large-granularity scanning method, while the target loss and recapture phase uses a narrow-range, small-granularity scanning method.

[0017] For step 102, the scanning mechanism is driven to move to the target scanning point according to the initial scanning trajectory based on the received scanning tracking command, and remains stationary at the position for a preset asynchronous sampling time.

[0018] Ranging based on asynchronous sampling dual optical combs involves electronic circuitry measuring distances over time that is thousands of times longer than the actual flight time. This measurement time is no longer negligible; the scanning mechanism must remain at a single measurement position for a sufficient period to ensure the accuracy and reliability of the measured distance value. The biggest difference between this system and traditional laser scanning and tracking systems is that the time required for distance measurement is no longer insignificant; the scanning mechanism must remain at the measurement position long enough to complete the measurement.

[0019] In this embodiment of the invention, the asynchronous sampling duration It is calculated using the following formula: In the formula, The target distance; The repetition frequency of the ranging optical frequency comb; The repetition frequency of the sampling optical frequency comb; It is the speed of light.

[0020] For step 104, the laser interference signal is acquired and calculated using the dual-comb asynchronous sampling ranging optical path to obtain the target distance data corresponding to the current scanning point.

[0021] In this embodiment of the invention, the target distance data is obtained in the following manner: The laser beam output from the measurement optical frequency comb is split by the first beam splitter. One beam is transmitted to the reference arm to form a reference light echo, and the other beam is reflected by the scanning mechanism to the cooperative target to form a measurement light echo. Specifically, the measurement optical frequency comb is activated to output a mode-locked femtosecond laser pulse sequence with a fixed repetition frequency. This laser pulse sequence is then incident perpendicularly onto a first beam splitter positioned at a 45-degree angle between the normal and the incident ray. The first beam splitter performs fixed-ratio beam splitting on the incident measurement laser pulse sequence, dividing it into two mutually perpendicular laser beams: The first path is a reference beam. After being refracted by the first beam splitter, it is incident on the reference arm fixedly installed in the refraction path of the first beam splitter along a preset optical path. After the reference beam passes through the reference optical path of the reference arm, it is reflected along the original optical path by the reference mirror at the end of the reference arm to form a reference light echo. The reference light echo returns to the first beam splitter after passing through the reference arm again, and is then transmitted to the second beam splitter through the first beam splitter. The second path is the measurement light beam. After being transmitted through the first beam splitter, it is incident on the optical reflecting mirror of the scanning mechanism, which is in a stationary state, along the preset light path. At this time, the scanning mechanism has been stably locked at the two-dimensional deflection angle of the designated scanning point. The measurement light beam is accurately projected onto the corresponding test area of ​​the cooperative target through mirror reflection. After being reflected by the surface of the cooperative target, the measurement light beam returns to the reflecting mirror of the scanning mechanism along the original incident light path. After being reflected twice by the mirror, it returns to the first beam splitter along the original light path. After being reflected by the first beam splitter, it is transmitted to the second beam splitter, forming a measurement light echo.

[0022] The reference light echo, the measurement light echo, and the laser output from the sampling light frequency comb are combined and interfered by the second beam splitter to generate the reference pulse interference signal packet and the measurement pulse interference signal packet.

[0023] Specifically, the sampling optical frequency comb is started synchronously, so that its output has a small fixed repetition frequency difference with the measurement optical frequency comb. The sampling laser pulse sequence is incident on the second beam splitter, which is arranged at an angle of 135 degrees between the normal and the incident light, along the preset optical path. At the same time, the reference light echo pulse sequence and the measurement light echo pulse sequence transmitted from the first beam splitter are synchronously incident on the beam combining optical path of the second beam splitter. The incident sampling laser pulse sequence, reference light echo pulse sequence, and measurement light echo pulse sequence are spatially combined and temporally matched by a second beam splitter, so that the sampling laser pulse sequence completely overlaps the reference light echo pulse sequence and the measurement light echo pulse sequence in the spatial domain and achieves periodic overlap matching in the temporal domain. Utilizing the asynchronous optical sampling effect caused by the small repetition rate difference between the measurement optical frequency comb and the sampling optical frequency comb, the reference optical echo pulse and the measurement optical echo pulse are linearly time-domain swept and sampled by the sampling laser pulse, so that the optical frequency domain information of the two sets of echo pulses is linearly mapped to the radio frequency domain that can be accurately measured by the circuit. In the output optical path of the second beam splitter, the reference pulse interference signal sequence and the measurement pulse interference signal sequence are generated respectively. After the two sets of interference signal sequences are accumulated and coherently superimposed in the time domain for a preset asynchronous sampling time, the reference pulse interference signal packet and the measurement pulse interference signal packet with complete envelope and signal-to-noise ratio that meet the measurement requirements are formed respectively. The two sets of packets are synchronously transmitted to the asynchronous sampling circuit.

[0024] The two interference packets are sampled asynchronously by an asynchronous sampling circuit. The time difference between the two packets is calculated, and the actual flight time difference is obtained by combining the frequency parameters of the optical frequency comb. Finally, the target distance data corresponding to the current scanning point is calculated.

[0025] Specifically, through an asynchronous sampling circuit, the input reference pulse interference signal packet and the measurement pulse interference signal packet are synchronously processed by high-bandwidth analog-to-digital conversion to complete the digital sampling and acquisition of the two sets of packets, and obtain the digital time-domain waveform data of the corresponding reference and measurement packets. Two sets of digitized time-domain waveform data are sequentially processed using digital filtering for noise reduction, baseline correction, envelope fitting, and peak localization. Circuit noise and optical clutter interference are filtered out, and the complete envelope curves of the two wave packets are accurately fitted. The time-domain positions T1 corresponding to the peak value of the reference pulse interference signal wave packet and T2 corresponding to the peak value of the measured pulse interference signal wave packet are located respectively. The time-domain interval ΔT = T2 - T1 between the peak values ​​of the two wave packets is calculated. This ΔT is the measurement time difference after optical amplification. Figure 2 As shown, the rising edge of SYNC1 provides the two-dimensional angle of the fast-reflecting mirror, and the rising edge of SYNC2 acquires the distance value, obtaining the ranging value corresponding to the two-dimensional angle. Then, the fast-reflecting mirror scans to the next position. In this embodiment, T1 is 2ms and T2 is 1.9ms.

[0026] Based on the pre-configured measurement optical comb repetition frequency f1 and sampling optical comb repetition frequency f2, the time amplification factor M is calculated:

[0027] Divide the magnified measurement time difference ΔT by the time magnification factor M to obtain the true flight time difference Δt. This true flight time difference is the difference between the flight time of the measurement light traveling between the system optical center and the cooperative target and the flight time of the reference light traveling between the system optical center and the reference arm end reference reflector. Combining the constant speed of light c in vacuum and the reference optical length L0 of the reference arm, the distance can be calculated using the following formula:

[0028] The high-precision absolute distance value of the cooperative target corresponding to the current scanning point is calculated, and the signal processing and data output of a single ranging measurement are completed.

[0029] For step 106, based on whether stable and valid target distance data has been obtained, it is determined whether the cooperative target has been successfully tracked, and the cooperative target is continuously tracked based on the determination result.

[0030] In this embodiment of the invention, if a stable and valid target distance value is calculated within the asynchronous sampling time, it is determined that the cooperative target has been successfully tracked, and the cooperative target is continuously tracked.

[0031] Specifically, after confirming successful tracking of the cooperative target, the drive scanning mechanism continuously scans and measures the target point by point according to the preset tracking scanning trajectory, and simultaneously collects and outputs the target's real-time high-precision distance data and corresponding angle position information to complete the continuous tracking of the cooperative target.

[0032] For example, the scanning mechanism scans using a Lissajous curve trajectory, scanning in a sinusoidal manner in both directions:

[0033] In this embodiment, m is 10, n is 9, and T is 1 / 10s during the initial tracking scan. The scan amplitude in the X direction. This refers to the scan amplitude in the Y direction. The fast-reflecting mirror has a scan frequency of 100Hz in the X direction and 90Hz in the Y direction. For example... Figure 3 As shown.

[0034] If a stable and valid target distance value is not calculated, it is determined that the cooperative target has not been tracked or the target has been lost, and the cooperative target will be recaptured.

[0035] Specifically, after determining that the cooperative target has been lost, the scanning parameters are switched to those of the target loss and recapture phase, starting from the last valid scanning point locked before the target was lost. Then, a rescan is performed, and the stationing, ranging and target determination are completed point by point until the cooperative target is tracked again.

[0036] For example, when re-tracking after a tracking failure, m is 10, n is 9, and T is 1 / 30s. The scan amplitude in the X direction. This represents the scanning amplitude in the Y direction, ranging from 0.1° to 7.5°. The fast-reflecting mirror has a scanning frequency of 300Hz in the X direction and 270Hz in the Y direction. For example... Figure 4 As shown.

[0037] like Figure 5 As shown, this embodiment of the invention also provides a high-precision tracking and ranging system for cooperative targets, applied to the method described in any of the above embodiments. The system includes a parallel-arranged measurement optical comb and a sampling optical comb, as well as a scanning mechanism, wherein: The first beam splitter and the reference arm are arranged sequentially along the optical path propagation direction of the measurement optical frequency comb, and the reference arm is set in the refraction optical path of the first beam splitter. The second beam splitter and the asynchronous sampling circuit are sequentially arranged along the optical path propagation direction of the sampling optical frequency comb; The scanning mechanism is located in the transmission optical path of the first beam splitter, and the scanning mechanism driver, control circuit and asynchronous sampling circuit are electrically connected.

[0038] The normal of the first beam splitter forms a 45-degree angle with the incident ray, and the normal of the second beam splitter forms a 135-degree angle with the incident ray.

[0039] It is worth noting that, in order to facilitate high-precision distance measurement, the cooperative target is equipped with a corner reflector. Cooperative target distance measurement generally refers to the corner reflector, which determines that the scanning angle of the scanning mechanism for tracking and measuring the cooperative target is generally small. In particular, high-precision distance measurement generally has a preliminary alignment, and the angle generally does not exceed 5 degrees.

[0040] Furthermore, the high-precision tracking and ranging system for cooperative targets provided in the above embodiments and the high-precision tracking and ranging method for cooperative targets belong to the same concept. For details of its specific implementation process, please refer to the method embodiments, which will not be repeated here.

[0041] Finally, it should be noted that in this document, relational terms such as first, second, third, and fourth are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0042] The above description is only a preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A high-precision tracking and ranging method for cooperative targets, characterized in that, The method includes: Based on the expected distance and ranging accuracy requirements of the cooperative target, the measurement optical comb and sampling optical comb are initialized to determine the scanning trajectory and scanning parameters for the initial scanning stage, the tracking scanning stage, and the target loss and recapture stage. According to the received scanning tracking command, the scanning mechanism is driven to move to the target scanning point along the initial scanning trajectory and stays at the position for a preset asynchronous sampling time. The laser interference signal is acquired and calculated using the dual-comb asynchronous sampling ranging optical path to obtain the target distance data corresponding to the current scanning point. Based on whether stable and valid target distance data has been obtained, it is determined whether the cooperative target has been successfully tracked, and the cooperative target is continuously tracked based on the determination result.

2. The method of claim 1, wherein, The initial scan trajectory, the tracking scan trajectory, and the recapture scan trajectory all adopt any one of the following: zigzag scan, Lissajous scan, or a custom optical scan trajectory.

3. The method of claim 1, wherein, The initial scanning phase employs a wide-range, large-granularity scanning method, while the target loss and recapture phase employs a narrow-range, small-granularity scanning method.

4. The method as described in claim 1, characterized in that, the asynchronous sampling duration is calculated by the following equation: wherein is the target distance; is the repetition frequency of the ranging optical frequency comb; is the repetition frequency of the sampling optical frequency comb; is the speed of light.

5. The method of claim 1, wherein, The process of acquiring and calculating the laser interference signal based on the dual-comb asynchronous sampling and ranging optical path to obtain the target distance data corresponding to the current scanning point includes: The laser output from the measurement optical frequency comb is split by the first beam splitter. One path is transmitted to the reference arm to form a reference light echo, and the other path is reflected by the scanning mechanism to the cooperative target to form a measurement light echo. The reference light echo, the measurement light echo, and the laser output from the sampling light frequency comb are combined and interfered by the second beam splitter to generate the reference pulse interference signal packet and the measurement pulse interference signal packet. The two interference packets are sampled asynchronously by an asynchronous sampling circuit. The time difference between the two packets is calculated, and the actual flight time difference is obtained by combining the frequency parameters of the optical frequency comb. Finally, the target distance data corresponding to the current scanning point is calculated.

6. The method of claim 1, wherein, The step of determining whether the cooperative target has been successfully tracked based on whether stable and valid target distance data has been obtained, and continuously tracking the cooperative target based on the determination result, includes: If a stable and valid target distance value is obtained within the asynchronous sampling period, it is determined that the cooperative target has been successfully tracked, and the cooperative target is continuously tracked. If a stable and valid target distance value is not calculated, it is determined that the cooperative target has not been tracked or the target has been lost, and the cooperative target will be recaptured.

7. The method of claim 6, wherein, The continuous tracking of cooperation goals includes: After successfully tracking the cooperative target, the drive scanning mechanism continuously scans and measures the target point by point according to the preset tracking scanning trajectory, and simultaneously collects and outputs the target's real-time high-precision distance data and corresponding angle position information to complete the continuous tracking of the cooperative target.

8. The method of claim 7, wherein, The process of recapturing a lost cooperative target includes: After determining that the cooperative target has been lost, the scanning parameters are switched to those of the target loss and re-acquisition phase, starting from the last valid scan point locked before the target was lost. Then, a rescan is performed, and the stationing, ranging and target determination are completed point by point until the cooperative target is tracked again.

9. A high-precision tracking and ranging system for cooperative targets, characterized in that, The system, applied to the method as described in any one of claims 1-8, comprises a measurement optical frequency comb and a sampling optical frequency comb arranged in parallel, and a scanning mechanism, wherein: The first beam splitter and the reference arm are arranged sequentially along the optical path propagation direction of the measurement optical frequency comb, and the reference arm is set in the refraction optical path of the first beam splitter. The second beam splitter and the asynchronous sampling circuit are sequentially arranged along the optical path propagation direction of the sampling optical frequency comb; The scanning mechanism is located in the transmission optical path of the first beam splitter, and the scanning mechanism driver, control circuit and asynchronous sampling circuit are electrically connected.

10. The system of claim 9, wherein, The normal of the first beam splitter forms a 45-degree angle with the incident ray, and the normal of the second beam splitter forms a 135-degree angle with the incident ray.

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