High-precision laser ranging system and method based on multi-frequency modulation

Abstract

The invention discloses a high-precision laser ranging system and method based on multi-frequency modulation, and relates to the field of laser ranging, and the system comprises a multi-frequency laser transmitting module which comprises generators of different frequency bands and can be independently regulated, rapidly switched and matched with a high-precision frequency modulation unit; the laser receiving and signal conditioning module is used for processing signals by using an avalanche photodiode, a low-noise preamplifier and the like; the signal processing and analyzing module is used for calculating the distance by means of a high-speed digital signal processor in combination with a multi-frequency distance measurement algorithm; a display and control module and a temperature compensation module are further included, the method comprises the steps of multi-frequency laser emission, receiving conditioning, signal processing, display control and temperature compensation, and high-precision distance measurement is achieved through fine operation according to environment and target characteristics. The method is high in distance measurement precision, and error compensation in a complex environment exceeds 90%; the adaptability is high, and automatic adjustment is achieved in different distances and environments; the real-time performance is good, and a result can be obtained within 10 milliseconds; operation is convenient, wireless and data management is supported, and laser ranging innovation is promoted.

Description

Technical Field

[0001] The present invention relates to the technical field of laser distance measurement, and in particular to a high-precision laser distance measurement system and method based on multi-frequency modulation. Background Art

[0002] With the rapid development of science and technology, laser ranging technology has shown extremely high application value in many fields, from precision measurement in industrial manufacturing, distance control in construction, to vehicle spacing monitoring in intelligent transportation systems, and target positioning in military defense, all of which are inseparable from the support of laser ranging. However, traditional laser ranging technology has gradually exposed many limitations in the face of growing high-precision requirements.

[0003] Early laser ranging mostly used single-frequency lasers, and its ranging principle was based on the measurement of the laser round-trip time. It emitted a pulsed laser and recorded the time difference of receiving the reflected light, and then calculated the distance in combination with the speed of light. However, this method is very susceptible to interference in complex environments, such as when there is smoke, dust, strong light interference, or when measuring distant targets. On the one hand, single-frequency laser signals are easily confused with stray light and noise in the environment, making it difficult for the receiving end to accurately identify effective signals, greatly reducing the ranging accuracy, and the error can even reach several meters, which is far from meeting the requirements of millimeter-level accuracy such as precision machining and high-precision mapping.

[0004] On the other hand, traditional laser ranging systems lack flexibility when dealing with targets at different distances. Due to the fixed characteristics of single-frequency lasers, it is impossible to simultaneously take into account both measurement accuracy and signal strength for targets that are closer or farther away. When measuring at close range, excessively high transmission power can easily cause energy waste and may also damage sensitive components at close range; when measuring at long distances, the signal is severely attenuated, making it difficult to receive reflected light of sufficient intensity, resulting in ranging failure or large errors.

[0005] Furthermore, the impact of ambient temperature changes on laser ranging systems cannot be ignored. The wavelength of the laser, the response characteristics of the photodetector, and the performance of the electronic components will change with temperature fluctuations, thus affecting the ranging accuracy. Traditional systems often lack an effective temperature compensation mechanism. In environments with large temperature differences, such as outdoor scenes with large temperature differences between morning and evening or high-temperature and low-temperature workshops in industrial production, the ranging error will increase significantly and the stability will be poor.

[0006] In addition, with the increasing demand for automated, intelligent production and monitoring, there are higher expectations for the real-time, convenience and versatility of laser ranging systems. Traditional systems have shortcomings in data processing speed, human-computer interaction convenience and the ability to work in coordination with other devices. They cannot quickly adapt to complex and changing work scenarios, which limits their further promotion and application.

[0007] In summary, in order to overcome these drawbacks, a new high-precision laser ranging system and method based on multi-frequency modulation is urgently needed to meet the urgent needs of modern fields for high-precision, highly adaptable, and intelligent laser ranging, and promote the technological progress and development of related industries. Summary of the invention

[0008] The present invention proposes a high-precision laser ranging system and method based on multi-frequency modulation to solve the problems mentioned in the above-mentioned prior art.

[0009] In order to achieve the above object, the present invention adopts the following technical solution: a high-precision laser ranging system based on multi-frequency modulation, comprising: Multi-frequency laser emission module: equipped with at least three laser generators with different frequencies, namely, a crystal oscillator driven laser generator with a low frequency band of 10MHz-50MHz, which uses a quartz crystal as a frequency reference, a voltage-controlled oscillator VCO laser generator with a medium frequency band of 50MHz-200MHz, and a phase-locked loop PLL laser generator with a high frequency band of 200MHz-1GHz. Through a high-precision phase detector and loop filter, the phase noise is lower than -100dBc / Hz. The laser generators in each frequency band are independently regulated and have a fast switching function, which can switch instantly between different frequencies according to the ranging requirements. Connect the frequency modulation unit, which uses direct digital frequency synthesis DDS technology based on field programmable gate array FPGA. The built-in phase accumulator has a bit number of no less than 32 bits, and the modulation depth is set within the range of 10%-90%. Suppose the modulation signal frequency is , the carrier frequency is , then the modulated laser frequency , the required modulation depth can be achieved through precise control. The modulation depth calculation formula is: ,in is the modulation signal amplitude, is the carrier amplitude; Laser receiving and signal conditioning module: Avalanche photodiode APD is used as the photodetector, and the photosensitive surface is treated with anti-reflection coating. The coating material is a multi-layer alternating structure of silicon nitride and silicon dioxide, which converts the received laser signal into an electrical signal; It is equipped with a low-noise preamplifier to amplify and reduce the noise of the electrical signal output by the photodetector. It is connected to a bandpass filter, which adopts a combination of a surface acoustic wave (SAW) filter and a ceramic filter. The center frequency is adaptively adjusted according to the frequency of the emitted laser to filter out the effective signal and remove the clutter interference. At the same time, an automatic gain control (AGC) circuit is also provided after the bandpass filter. Suppose the input signal power is , the output signal power is , the AGC gain calculation formula is: ; Signal processing and analysis module: built-in high-speed digital signal processor DSP, multi-core architecture, real-time acquisition and processing of conditioned electrical signals, use fast Fourier transform FFT algorithm to perform spectrum analysis on the signal, extract the amplitude and phase information of different frequency components, set the round-trip time of different frequency lasers to be , the corresponding frequency is , construct the objective function according to the least squares method Where c is the speed of light, d is the target distance, and the target distance is obtained by solving the value of d that minimizes J; Display and control module: It has a visual liquid crystal display LCD, adopts TFT-LCD technology, and the display screen also has a backlight adjustment function, which automatically adjusts the backlight brightness according to the ambient light intensity; It has human-computer interaction function and is operated through buttons or touch screen. The buttons are made of waterproof, dustproof and wear-resistant silicone material. The touch screen is a capacitive touch screen. At the same time, the system automatically adjusts the working status of each module according to user instructions.

[0010] Furthermore, in the multi-frequency laser emission module, each laser generator adopts a fiber-coupled output mode to reduce energy loss during transmission. The optical fiber adopts a special low-loss quartz optical fiber, whose attenuation coefficient within the laser wavelength range does not exceed 0.2dB / km, and the outer jacket adopts polyetheretherketone PEEK material.

[0011] Furthermore, in the laser receiving and signal conditioning module, an optical focusing lens group is arranged in front of the avalanche photodiode APD. The lens group adopts an achromatic doublet lens with a focal length between 10mm-50mm to focus the received laser beam onto the photosensitive surface of the APD.

[0012] Furthermore, in the signal processing and analysis module, when using the fast Fourier transform FFT algorithm, the windowing function technology is adopted. At the same time, after the spectrum analysis, the spectrum is processed again by the spectrum peak search algorithm. This algorithm is based on peak detection and interpolation technology, which reduces the distance calculation error by 20%-30%. Assume that the peak frequency of the original spectrum is , the frequency corrected by the spectrum peak search algorithm is , correction amount ,pass Control to optimize distance calculations.

[0013] Furthermore, in the display and control module, the system supports wireless connection with external devices. During the wireless transmission process, the encryption standard AES256-bit encryption algorithm is used to encrypt the data. The system also supports connection with the host computer software, which is developed based on the Windows or Linux platform.

[0014] Furthermore, the system also includes a temperature compensation module with a built-in temperature sensor to monitor the system working environment temperature in real time. The temperature compensation module adopts a compensation model based on a neural network. By learning and training the temperature and ranging error data, the temperature and laser frequency, photoelectric detector response, and signal processing parameters are constructed. The temperature change is , the compensated laser frequency is , the photodetector response parameters are , the signal processing parameters are , the specific formula is: .

[0015] Furthermore, a method for applying the high-precision laser ranging system based on multi-frequency modulation comprises the following steps: Multi-frequency laser emission steps: According to the distance range and environmental characteristics of the target to be measured, select a laser generator from the system's multi-frequency laser emission module, use the frequency modulation unit to frequency modulate the selected laser, carry the information required for ranging, and emit the laser beam with a preset pulse width and repetition frequency. Before emission, the laser generator needs to be preheated and calibrated. Suppose the laser pulse energy is E and the pulse width is , transmit power ; Laser receiving and signal conditioning steps: The avalanche photodiode APD in the laser receiving and signal conditioning module receives the reflected laser signal, converts it into an electrical signal, initially amplifies and reduces noise through a low-noise preamplifier, and then filters out the effective signal corresponding to the emission frequency through a bandpass filter. Suppose the original signal strength is The enhanced signal strength is , signal enhancement factor , through control to ensure that the signal can be effectively processed by subsequent modules; Signal processing and analysis steps: The high-speed digital signal processor DSP of the signal processing and analysis module collects the conditioned electrical signal in real time, uses the fast Fourier transform FFT algorithm combined with the windowing function technology to perform spectrum analysis, and extracts the amplitude and phase information of laser signals of different frequencies. According to the multi-frequency ranging algorithm, if an abnormal frequency signal is found during the calculation process, the frequency data is automatically removed, and the remaining frequency data is used for recalculation. The amplitude of the different frequency signals obtained by the spectrum analysis is set to , the phase is , and substitute it into the multi-frequency ranging algorithm formula based on the least squares method to solve the target distance; Display and control steps: The calculated target distance, location, laser frequency, and signal strength information are displayed in real time on the LCD screen of the display and control module. The user adjusts the system parameters through the human-computer interaction interface. The power consumption before the system is set to P before , the power consumption after standby is Pafter , power consumption reduction ratio , low power standby is achieved by controlling r; Temperature compensation steps: The temperature sensor in the temperature compensation module monitors the ambient temperature in real time. When the temperature changes, the system automatically calls the pre-stored temperature compensation model and makes corresponding adjustments to the laser frequency, photodetector response characteristics, signal processing parameters, etc. The original ranging error is set to , the distance measurement error after compensation is , error reduction ratio , the temperature compensation effect is evaluated by controlling s.

[0016] Furthermore, in the multi-frequency laser emission step, when there is interference in the ranging environment, the frequency of the emitted laser is automatically increased to enter the high frequency band of 200MHz-1GHz, and the strong anti-interference ability of the high-frequency laser is used to reduce the impact of strong light on the ranging signal. At the same time, the power of the emitted laser is increased by 20%-50% on the original basis. The pulse code modulation PCM technology is also used to encode the emitted laser. The encoding method is Gray code or Manchester code. The strong light intensity is set to , the laser power increase and The relationship between is obtained by fitting the experimental data, such as , k is the fitting coefficient.

[0017] Furthermore, in the signal processing and analysis step, for the long-distance ranging scenario, the number of signal sampling points is increased, and the long signal is analyzed by segmented processing. The long signal is divided into 3-5 segments, and each segment is subjected to FFT operation and subsequent processing. Finally, the final distance is obtained by combining the results of each segment. In the segmented processing process, the overlap-addition method is used to process the adjacent segment signals. Assume that the original number of sampling points is , the number of sampling points after increase , where r is the ratio of the increase in the number of sampling points, and r is selected according to the long-distance ranging requirements.

[0018] Compared with the prior art, the present invention has the following beneficial effects: In terms of precision improvement, through the multi-frequency laser emission module, the use of laser ranging at different frequencies and combined with the multi-frequency ranging algorithm, the round-trip time difference and phase change of lasers at each frequency are comprehensively considered to effectively offset the errors caused by environmental interference, and the ranging accuracy is precisely controlled between ±0.1mm-±1mm. Even in complex environments, the error compensation capability can reach more than 90%, providing reliable measurement guarantee for precision manufacturing, high-end surveying and mapping and other fields.

[0019] It has excellent adaptability. When facing targets at different distances, it can select frequency combinations as needed. Low frequency is used to save energy at close range, and high frequency is used to ensure accuracy at long distances. When encountering strong light interference, it automatically increases the frequency and power and encodes to enhance anti-interference ability. When the ambient temperature fluctuates, the temperature compensation module dynamically adjusts parameters according to the neural network model to ensure stable ranging accuracy. It can accurately measure distance regardless of outdoor operations in severe cold or heat, or in industrial environments with large temperature differences.

[0020] The system has strong real-time performance, with a high-speed digital signal processor and optimized algorithm, more than 100 spectrum analyses per second, ranging results within 10 milliseconds in complex environments, and real-time feedback on measurement conditions to meet the needs of rapid decision-making scenarios such as automated production lines and intelligent transportation.

[0021] It has good convenience and expandability, with visual display and convenient human-computer interaction, and is easy to operate; it supports multiple languages, wireless connection and host computer collaboration, which facilitates remote control and data sharing; the data storage and export functions are conducive to traceability analysis, providing data support for subsequent process improvement and troubleshooting, and promoting the innovation and application expansion of laser ranging technology in all directions. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A schematic block diagram of a high-precision laser ranging system based on multi-frequency modulation proposed by the present invention; Figure 2 The present invention provides a schematic block diagram of a high-precision laser ranging method based on multi-frequency modulation. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0025] In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined. In addition, the terms "installed", "connected" and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, and it can be the internal connection of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances. The present invention will be further described in detail below in conjunction with the accompanying drawings.

[0026] Reference Figure 1-2 :A high-precision laser ranging system based on multi-frequency modulation, comprising: Multi-frequency laser emission module: equipped with at least three laser generators of different frequencies, including low-frequency 10MHz-50MHz crystal oscillator driven laser generator, which uses quartz crystal as frequency reference and has a frequency stability of ±1ppm; medium-frequency 50MHz-200MHz voltage-controlled oscillator VCO laser generator, which achieves fast frequency fine-tuning through precise voltage regulation, with an adjustment sensitivity of 1MHz / V; high-frequency 200MHz-1GHz phase-locked loop PLL laser generator, with high-precision phase detector and loop filter, phase noise is lower than -100dBc / Hz, and locking time does not exceed 50 microseconds. Each frequency band laser generator can be independently regulated, the output power is stable within the fluctuation range of ±5%, and has a fast switching function, the switching time does not exceed 100 microseconds, and can switch instantly between different frequencies according to the distance measurement requirements. The divergence angle of the emitted laser beam is controlled between 0.1mrad-1mrad to ensure the collimation and energy concentration of the laser beam.

[0027] It is connected to a high-precision frequency modulation unit, which uses direct digital frequency synthesis DDS technology and is implemented based on a field programmable gate array FPGA. Its built-in phase accumulator has a bit number of no less than 32 bits and a frequency resolution of up to 1Hz. It finely modulates the laser frequency so that the emitted laser carries rich frequency information. The modulation depth can be set as needed within the range of 10%-90%, meeting the frequency change requirements of different ranging scenarios. The frequency modulation unit also has a frequency scanning function. The scanning step can be set to 1Hz-10Hz, and the scanning rate is between 100Hz / s-1kHz / s, which is convenient for detecting the target frequency response characteristics before ranging. Assume that the modulation signal frequency is , the carrier frequency is , then the modulated laser frequency , the required modulation depth can be achieved through precise control. The modulation depth calculation formula is: ,in is the modulation signal amplitude, is the carrier amplitude.

[0028] Laser receiving and signal conditioning module: A highly sensitive avalanche photodiode APD is used as the photodetector. Its photosensitive surface is treated with a special anti-reflection coating. The coating material is a multi-layer alternating structure of silicon nitride and silicon dioxide, which can reduce the reflectivity to below 1%. The response time does not exceed 1 nanosecond, and the quantum efficiency is in the range of 60%-90%. It can quickly and efficiently convert the received weak laser signal into an electrical signal.

[0029] It is equipped with a low-noise preamplifier, using low-noise transistors and optimized circuit layout design, with a noise figure lower than 3dB and a gain range of 20dB-60dB. It performs preliminary amplification and noise reduction on the electrical signal output by the photodetector to ensure that the signal-to-noise ratio is improved by at least 20dB. It is subsequently connected to a bandpass filter, which uses a combination of a surface acoustic wave (SAW) filter and a ceramic filter. The center frequency is adaptively adjusted according to the frequency of the emitted laser, and the bandwidth is between 1dB-10dB, which can accurately filter out effective signals and remove clutter interference. At the same time, an automatic gain control (AGC) circuit is also provided after the bandpass filter, with a dynamic range of not less than 40dB. It can automatically adjust the gain according to the input signal strength to ensure that the signal amplitude received by the subsequent processing unit is relatively stable. Assume that the input signal power is , the output signal power is , the AGC gain calculation formula is: ; Signal processing and analysis module: Built-in high-speed digital signal processor DSP, multi-core architecture, single-core processing capacity of not less than 1GHz, can collect and process conditioned electrical signals in real time, use fast Fourier transform FFT algorithm to perform spectrum analysis on signals, and extract amplitude and phase information of different frequency components. When performing FFT calculation, a mixed calculation method of fixed-point and floating-point numbers is used, taking into account both calculation speed and accuracy, and the analysis and processing speed reaches more than 100 times per second, ensuring the real-time performance of ranging.

[0030] Combined with the multi-frequency ranging algorithm, the algorithm fits and solves the round-trip time difference and phase change of lasers with different frequencies based on the least squares method, and comprehensively calculates the target distance. The algorithm accuracy is between ±0.1mm-±1mm, and the ranging error compensation capability in complex environments reaches more than 90%, effectively improving the accuracy of ranging. Assume that the round-trip time of lasers with different frequencies is , the corresponding frequency is , construct the objective function according to the least squares method Where c is the speed of light, d is the target distance, and the target distance is obtained by solving the value of d that minimizes J. At the same time, the signal processing and analysis module also has a self-diagnosis function, monitoring key system parameters such as signal strength, frequency stability, phase noise, etc. every 10 seconds. Once an abnormality is found, an alarm is issued in time and automatic repair is attempted, with a repair success rate of no less than 80%.

[0031] Display and control module: It has a visual LCD display, adopts high-resolution TFT-LCD technology, and has a pixel density of no less than 300ppi. It can display key parameters such as measured distance, laser frequency, and signal strength in real time, and the display refresh rate is no less than 10Hz, allowing users to intuitively understand the distance measurement situation. The display also has a backlight adjustment function, which can automatically adjust the backlight brightness according to the ambient light intensity, improve visibility by 50% in strong light, and reduce power consumption by 30% in weak light.

[0032] It has human-computer interaction function and can be operated by buttons or touch screen. The buttons are made of waterproof, dustproof and wear-resistant silicone material. The touch screen is a capacitive touch screen with a touch response sensitivity of not less than 0.1 second. Users can easily set the laser frequency, modulation parameters, ranging mode, etc. At the same time, the system can automatically adjust the working status of each module according to user instructions to achieve intelligent control. In addition, the display and control module also supports multi-language display, covering at least 5 common languages ​​such as Chinese, English, Japanese, and German, which is convenient for users in different regions.

[0033] In the present invention, in the multi-frequency laser emission module, each laser generator adopts the fiber coupling output mode, and the coupling efficiency is not less than 80%, ensuring the efficient transmission of laser energy and reducing the energy loss in the transmission process. The optical fiber adopts special low-loss quartz optical fiber, and its attenuation coefficient within the laser wavelength range does not exceed 0.2dB / km, and the optical fiber has good flexibility. The outer jacket adopts high-strength polyetheretherketone PEEK material, which can withstand bending times of not less than 10,000 times, which is convenient for the installation and layout of the system.

[0034] In the present invention, in the laser receiving and signal conditioning module, an optical focusing lens group is arranged in front of the avalanche photodiode APD. The lens group adopts an achromatic double glued lens with a focal length between 10mm and 50mm, which can focus the received laser beam onto the photosensitive surface of the APD, improve the collection efficiency of the optical signal, and improve the photoelectric conversion effect by more than 30%. The lens group is also equipped with an electric focusing function. Driven by a motor, the focusing accuracy can reach ±0.1mm. The focal length can be automatically adjusted according to the distance of the target to optimize the optical signal reception effect.

[0035] In the present invention, in the signal processing and analysis module, when using the fast Fourier transform FFT algorithm, the window function technology is adopted, and the Hanning window or the Blackman window is selected. The window function length is adaptively adjusted according to the signal length, and the adjustment step is 1 / 10 of the signal length. At the same time, after the spectrum analysis, the spectrum is secondary processed by the spectrum peak search algorithm. The algorithm is based on peak detection and interpolation technology, which can improve the spectrum peak positioning accuracy to within 0.1Hz, effectively reduce spectrum leakage, improve the accuracy of spectrum analysis, and further reduce the distance calculation error by 20%-30%. Assume that the peak frequency of the original spectrum is , the frequency corrected by the spectrum peak search algorithm is , correction amount ,pass Control to optimize distance calculations.

[0036] In the present invention, in the display and control module, the system supports wireless connection with external devices, adopts Bluetooth 5.0 or Wi-Fi6 technology, and the wireless transmission rate is not less than 10Mbps, and the measurement data can be transmitted to mobile phones, computers and other terminal devices in real time. During the wireless transmission process, the data is encrypted using the Advanced Encryption Standard AES256-bit encryption algorithm to ensure the security of data transmission. At the same time, the system also supports connection with the host computer software, which is developed based on the Windows or Linux platform and has functions such as data visualization analysis, remote control, and batch parameter setting, which facilitates remote viewing and further analysis of data.

[0037] In the present invention, the system also includes a temperature compensation module with a built-in high-precision temperature sensor. The temperature measurement accuracy reaches ±0.5°C, and the system working environment temperature is monitored in real time. The temperature compensation module adopts a compensation model based on a neural network. By learning and training a large amount of temperature and ranging error data, a complex nonlinear relationship between temperature and laser frequency, photodetector response, signal processing parameters, etc. is constructed. When the temperature changes, the relevant parameters are dynamically compensated according to the pre-stored neural network model. The compensation accuracy is between ±0.05mm-±0.5mm, ensuring the stability of the ranging accuracy of the system in different temperature environments. Assume that the temperature change is , the compensated laser frequency is , the photodetector response parameters are , the signal processing parameters are , the specific formula is: .

[0038] The present invention also discloses a high-precision laser ranging method based on multi-frequency modulation, comprising the following steps: Multi-frequency laser emission steps: According to the approximate distance range and environmental characteristics of the target to be measured, select a laser generator with a suitable frequency combination from the system's multi-frequency laser emission module. If the target distance is close and the environmental interference is small, low-frequency lasers are preferred to reduce power consumption; if the distance is far or the environment is complex, high-frequency lasers are combined to improve ranging accuracy and anti-interference capabilities. Use the frequency modulation unit to frequency modulate the selected laser, carry the information required for ranging, and emit a laser beam with a preset pulse width and repetition frequency. The pulse width is between 10ns-100ns, and the repetition frequency is between 1kHz-10kHz, ensuring that the emission parameters of the laser beam are adapted to the ranging scenario. Before emission, the laser generator must also be preheated and calibrated. The preheating time is between 10 seconds and 60 seconds depending on the laser type, and the calibration accuracy reaches ±0.1MHz to ensure the accuracy of the laser frequency. Assume that the laser pulse energy is E and the pulse width is , transmit power , by adjusting E and t p To meet different distance measurement needs.

[0039] Laser receiving and signal conditioning steps: The avalanche photodiode APD in the laser receiving and signal conditioning module receives the reflected laser signal, converts it into an electrical signal, and initially amplifies and reduces noise through a low-noise preamplifier. Then, the effective signal corresponding to the emission frequency is filtered out through a bandpass filter to provide a high-quality input signal for subsequent processing. The entire process is completed within microseconds to ensure the timeliness of the signal. When the received signal strength is too weak, the signal enhancement mode is automatically started to increase the signal strength to a processable range by increasing the preamplifier gain, extending the signal integration time, etc., to ensure the continuity of the ranging. Assume that the original signal strength is The enhanced signal strength is , signal enhancement factor , through control, it is ensured that the signal can be effectively processed by subsequent modules.

[0040] Signal processing and analysis steps: The high-speed digital signal processor DSP of the signal processing and analysis module collects the conditioned electrical signal in real time, uses the fast Fourier transform FFT algorithm combined with the windowing function technology to perform spectrum analysis, and extracts the amplitude and phase information of laser signals of different frequencies. Based on the multi-frequency ranging algorithm, the target distance is comprehensively calculated, and the ranging results can be given quickly and accurately in complex environments. The calculation time does not exceed 10 milliseconds. During the calculation process, if a certain frequency signal is found to be abnormal, such as spectrum distortion or phase jump, the frequency data is automatically eliminated, and the remaining frequency data is used for recalculation to ensure the reliability of the ranging results. Assume that the amplitude of the different frequency signals obtained by the spectrum analysis is , the phase is , substitute these values ​​into the multi-frequency ranging algorithm formula based on the least squares method to solve the target distance.

[0041] Display and control steps: The calculated target distance, location, laser frequency, signal strength and other information are displayed in real time on the LCD screen of the display and control module. The user can adjust the system parameters at any time through the human-computer interaction interface, such as switching the laser frequency, modifying the modulation depth, etc. The system responds immediately to user instructions and optimizes the ranging effect. When the user does not operate for a long time, the system automatically enters low-power standby mode, and the standby power consumption is reduced by 80%. Once an operation instruction or environmental change is detected, it will quickly wake up and resume normal working state. Assume that the system power consumption before standby is P before , the power consumption after standby is P after , power consumption reduction ratio , low power standby is achieved through control.

[0042] Temperature compensation steps: The high-precision temperature sensor in the temperature compensation module monitors the ambient temperature in real time. Once the temperature changes, the system automatically calls the pre-stored temperature compensation model to adjust the laser frequency, photodetector response characteristics, signal processing parameters, etc. During the temperature compensation process, the bilinear interpolation method is used to optimize the compensation parameters to increase the compensation accuracy by 10%-20% on the original basis, ensuring that the ranging accuracy is not affected by temperature fluctuations and maintaining the system's high-precision ranging performance. Assume that the original ranging error is , the distance measurement error after compensation is , error reduction ratio , the temperature compensation effect is evaluated through control.

[0043] In the present invention, in the multi-frequency laser emission step, when there is strong light interference in the ranging environment, the frequency of the emitted laser is automatically increased to enter the high frequency band of 200MHz-1GHz, and the strong anti-interference ability of the high-frequency laser is used to reduce the influence of the strong light on the ranging signal. At the same time, the power of the emitted laser is increased by 20%-50% on the original basis. The specific increase is adaptively adjusted according to the intensity of the strong light. The stronger the strong light, the greater the increase. In addition, pulse code modulation PCM technology is used to encode the emitted laser. The encoding method is Gray code or Manchester code. The ranging signal and the interference signal can be effectively distinguished through coding recognition to ensure that the reflected laser signal can be effectively received. Assume that the intensity of the strong light is , the laser power increase and The relationship between is obtained by fitting the experimental data, such as , k is the fitting coefficient, calculated in real time.

[0044] In the present invention, in the signal processing and analysis steps, for the long-distance ranging scenario, the number of sampling points of the signal is increased by 50%-100% on the original basis, and the long signal is analyzed by segmented processing. The long signal is divided into 3-5 segments, and each segment is subjected to FFT calculation and subsequent processing, and finally the final distance is obtained by combining the results of each segment. In the segmented processing process, the overlap-addition method is used to process adjacent segment signals, and the overlap ratio is 20%-30%, which reduces the error of spectrum analysis, improves the accuracy of long-distance ranging, and controls the error of long-distance ranging between ±1mm-±5mm. Assume that the original number of sampling points is , the number of sampling points after increase (r is the ratio of the increase in the number of sampling points). Select r reasonably according to the long-distance measurement requirements.

[0045] In the present invention, in the high-precision laser ranging system and method based on multi-frequency modulation, the display and control module of the system has a powerful data management function. On the one hand, it can automatically store the latest 100 ranging data, covering detailed information such as measurement time, precise distance value, laser frequency used and signal strength. The storage medium uses a high-speed and stable solid-state hard disk (SSD) to ensure the rapidity and high reliability of data reading and writing, and avoid the risk of data loss. On the other hand, users can easily initiate historical data query operations at any time through the human-computer interaction interface. The system ensures that the query response time does not exceed 1 second, and instantly calls out the required historical data and presents it to the user in a clear and intuitive manner, providing strong support for the accurate tracing and in-depth analysis of the ranging situation and the subsequent optimization of the ranging strategy. At the same time, the system also supports the data export function. Users can easily export the stored data to external storage devices such as U disk, mobile hard disk, etc. in a general CSV or Excel format according to their own needs, which is convenient for more comprehensive and in-depth data analysis in other professional software environments, further exploring the potential value of ranging data, and improving the practicality and expansibility of the entire ranging system.

[0046] The above are only preferred specific implementation modes of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and inventive concepts of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A high-precision laser ranging system based on multi-frequency modulation, characterized in that: include: Multi-frequency laser emission module: equipped with at least three laser generators with different frequencies, namely, a crystal oscillator driven laser generator with a low frequency band of 10MHz-50MHz, which uses a quartz crystal as a frequency reference, a voltage-controlled oscillator VCO laser generator with a medium frequency band of 50MHz-200MHz, and a phase-locked loop PLL laser generator with a high frequency band of 200MHz-1GHz. Through a high-precision phase detector and loop filter, the phase noise is lower than -100dBc / Hz. The laser generators in each frequency band are independently regulated and have a fast switching function, which can switch instantly between different frequencies according to the ranging requirements. Connect the frequency modulation unit, which uses direct digital frequency synthesis DDS technology based on field programmable gate array FPGA. The built-in phase accumulator has a bit number of no less than 32 bits, and the modulation depth is set within the range of 10%-90%. Suppose the modulation signal frequency is , the carrier frequency is , then the modulated laser frequency , the required modulation depth can be achieved through precise control. The modulation depth calculation formula is: ,in is the modulation signal amplitude, is the carrier amplitude; Laser receiving and signal conditioning module: Avalanche photodiode APD is used as the photodetector, and the photosensitive surface is treated with anti-reflection coating. The coating material is a multi-layer alternating structure of silicon nitride and silicon dioxide, which converts the received laser signal into an electrical signal; Signal processing and analysis module: built-in high-speed digital signal processor DSP, multi-core architecture, real-time acquisition and processing of conditioned electrical signals, use fast Fourier transform FFT algorithm to perform spectrum analysis on the signal, extract the amplitude and phase information of different frequency components, set the round-trip time of different frequency lasers to be , the corresponding frequency is , construct the objective function according to the least squares method Where c is the speed of light, d is the target distance, and the target distance is obtained by solving the value of d that minimizes J; Display and control module: It has a visual liquid crystal display LCD, adopts TFT-LCD technology, and the display also has a backlight adjustment function, which automatically adjusts the backlight brightness according to the ambient light intensity.

2. The high-precision laser ranging system based on multi-frequency modulation according to claim 1, characterized in that: In the multi-frequency laser emission module, each laser generator adopts fiber-coupled output to reduce energy loss during transmission. The optical fiber adopts special low-loss quartz optical fiber, whose attenuation coefficient within the laser wavelength range does not exceed 0.2dB / km, and the outer jacket adopts polyetheretherketone PEEK material.

3. The high-precision laser ranging system based on multi-frequency modulation according to claim 1, characterized in that: In the laser receiving and signal conditioning module, an optical focusing lens group is arranged in front of the avalanche photodiode APD. The lens group adopts an achromatic doublet lens with a focal length between 10mm and 50mm to focus the received laser beam onto the photosensitive surface of the APD. It is equipped with a low-noise preamplifier to amplify and reduce the noise of the electrical signal output by the photodetector. It is connected to a bandpass filter, which adopts a combination of a surface acoustic wave (SAW) filter and a ceramic filter. The center frequency is adaptively adjusted according to the frequency of the emitted laser to filter out the effective signal and remove the clutter interference. At the same time, an automatic gain control (AGC) circuit is also provided after the bandpass filter. Suppose the input signal power is , the output signal power is , the AGC gain calculation formula is: .

4. The high-precision laser ranging system based on multi-frequency modulation according to claim 1, characterized in that: In the signal processing and analysis module, when using the fast Fourier transform FFT algorithm, the window function technology is adopted. At the same time, after the spectrum analysis, the spectrum is processed again by the spectrum peak search algorithm. This algorithm is based on peak detection and interpolation technology, which reduces the distance calculation error by 20%-30%. Assume that the peak frequency of the original spectrum is , the frequency corrected by the spectrum peak search algorithm is , correction amount ,pass Control to optimize distance calculations.

5. The high-precision laser ranging system based on multi-frequency modulation according to claim 1, characterized in that: In the display and control module, the system supports wireless connection with external devices. During the wireless transmission process, the encryption standard AES256-bit encryption algorithm is used to encrypt the data. The system also supports connection with the host computer software, which is developed based on the Windows or Linux platform. It has human-computer interaction function and is operated through buttons or touch screen. The buttons are made of waterproof, dustproof and wear-resistant silicone material. The touch screen is a capacitive touch screen. At the same time, the system automatically adjusts the working status of each module according to user instructions.

6. The high-precision laser ranging system based on multi-frequency modulation according to claim 1, characterized in that: The system also includes a temperature compensation module with a built-in temperature sensor to monitor the system working environment temperature in real time. The temperature compensation module adopts a compensation model based on a neural network. By learning and training the temperature and ranging error data, it constructs the temperature and laser frequency, photoelectric detector response, and signal processing parameters. Suppose the temperature change is , the compensated laser frequency is , the photodetector response parameters are , the signal processing parameters are , the specific formula is: .

7. A method for applying the high-precision laser ranging system based on multi-frequency modulation according to any one of claims 1 to 6, characterized in that: The following steps are involved: Multi-frequency laser emission steps: According to the distance range and environmental characteristics of the target to be measured, select a laser generator from the system's multi-frequency laser emission module, use the frequency modulation unit to frequency modulate the selected laser, carry the information required for ranging, and emit the laser beam with a preset pulse width and repetition frequency. Before emission, the laser generator needs to be preheated and calibrated. Suppose the laser pulse energy is E and the pulse width is , transmit power ; Laser receiving and signal conditioning steps: The avalanche photodiode APD in the laser receiving and signal conditioning module receives the reflected laser signal, converts it into an electrical signal, initially amplifies and reduces noise through a low-noise preamplifier, and then filters out the effective signal corresponding to the emission frequency through a bandpass filter. Suppose the original signal strength is The enhanced signal strength is , signal enhancement factor ; Signal processing and analysis steps: The high-speed digital signal processor DSP of the signal processing and analysis module collects the conditioned electrical signal in real time, uses the fast Fourier transform FFT algorithm combined with the windowing function technology to perform spectrum analysis, and extracts the amplitude and phase information of laser signals of different frequencies. According to the multi-frequency ranging algorithm, if an abnormal frequency signal is found during the calculation process, the frequency data is automatically removed, and the remaining frequency data is used for recalculation. The amplitude of the different frequency signals obtained by the spectrum analysis is set to , the phase is , and substitute it into the multi-frequency ranging algorithm formula based on the least squares method to solve the target distance; Display and control steps: The calculated target distance, location, laser frequency, and signal strength information are displayed in real time on the LCD screen of the display and control module. The user adjusts the system parameters through the human-computer interaction interface. The power consumption before the system is set to P before , the power consumption after standby is P after , power consumption reduction ratio , low power standby is achieved by controlling r; Temperature compensation steps: The temperature sensor in the temperature compensation module monitors the ambient temperature in real time. When the temperature changes, the system automatically calls the pre-stored temperature compensation model and adjusts the laser frequency, photodetector response characteristics, and signal processing parameters accordingly. The original ranging error is set to , the distance measurement error after compensation is , the error reduction ratio , the temperature compensation effect is evaluated by controlling s.

8. The method of the high-precision laser ranging system based on multi-frequency modulation according to claim 7, characterized in that: In the multi-frequency laser emission step, when there is interference in the ranging environment, the frequency of the emitted laser is automatically increased to enter the high frequency band of 200MHz-1GHz. The strong anti-interference ability of high-frequency laser is used to reduce the impact of strong light on the ranging signal. At the same time, the power of the emitted laser is increased by 20%-50% on the original basis. Pulse code modulation PCM technology is also used to encode the emitted laser. The encoding method is Gray code or Manchester code. Suppose the intensity of strong light is , the laser power increase and The relationship between is obtained by fitting the experimental data, such as , k is the fitting coefficient.

9. The method of the high-precision laser ranging system based on multi-frequency modulation according to claim 7, characterized in that: In the signal processing and analysis step, for the long-distance ranging scenario, the number of signal sampling points is increased, and the long signal is analyzed by segmented processing. The long signal is divided into 3-5 segments, and each segment is subjected to FFT operation and subsequent processing. Finally, the final distance is obtained by combining the results of each segment. In the segmented processing process, the overlap-addition method is used to process the adjacent segment signals. Assume that the original number of sampling points is , the number of sampling points after increase , where r is the ratio of the increase in the number of sampling points, and r is selected according to the long-distance ranging requirements.

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