Multi-channel synchronous length measurement system and method based on laser FMCW technology

Abstract

The application relates to the field of laser measurement technology and discloses a multi-channel synchronous length measuring system and method based on laser FMCW technology, which comprises an FMCW measuring host, a tail fiber, a fiber splitter, fiber channels and an optical lens. The FMCW measuring host divides an effective bandwidth into multiple frequency regions by utilizing the optical path length difference set by multiple fiber channels. The fiber splitter distributes a single laser signal to multiple fiber channels. The echo signal is limited in the corresponding frequency region by utilizing different fiber lengths. The FMCW measuring host extracts the up-sweep beat frequency and the down-sweep beat frequency respectively, calculates the motion speed of the length cable to be measured by combining the spatial geometric projection relationship, and calculates the cumulative production length. The application realizes the synchronous monitoring of multiple production lines by a single device through the frequency domain isolation mechanism based on the optical path difference, avoids signal aliasing, and guarantees the signal independence of multi-channel parallel measurement.

Description

Technical Field

[0001] This invention relates to the field of laser measurement technology, specifically to a multi-channel synchronous length measurement system and method based on laser FMCW technology. Background Technology

[0002] In the production environments of cable manufacturing, textile printing and dyeing, and metallurgical rolling industries, real-time speed monitoring and length measurement of moving cables or plates are core process links. Traditional contact-type mechanical metering wheels rely on friction for drive. Mechanical metering wheels can slip at high speeds, leading to the accumulation of measurement errors. Furthermore, the physical contact of mechanical metering wheels can easily damage the surface of the object being measured. Non-contact laser velocimetry technology can avoid the damage and errors caused by physical contact, and has become the mainstream development direction for industrial online measurement.

[0003] When facing industrial sites with multiple production lines operating in parallel, existing laser velocimetry systems typically adopt a single-machine, single-channel working mode. In order to simultaneously monitor multiple cables of length to be measured, the manufacturing workshop needs to configure a complete laser measurement host and optical probe for each cable of length to be measured. The deployment method of configuring a measurement host for each cable of length to be measured increases the cost of hardware equipment and also increases the complexity of system integration and data synchronization.

[0004] If we try to simply use a single laser host to drive multiple measurement probes, the multiple echo signals will superimpose at the photodetector. Without an effective physical or signal layer isolation mechanism, the multiple echo signals will generate aliasing interference in the frequency domain. The signal aliasing makes it impossible for the signal processing unit to accurately distinguish the Doppler frequency shift information corresponding to different measurement channels. This makes it impossible to achieve synchronous and accurate measurement of multiple targets using a single laser source. Existing technologies cannot achieve both multi-channel parallel measurement and high signal-to-noise ratio signal extraction under a low-cost hardware architecture, which limits the large-scale application of laser measurement technology in multi-channel parallel production scenarios. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a multi-channel synchronous length measurement system and method based on laser FMCW technology. This solves the problems of increased equipment costs due to the need to configure a separate measurement host for each cable to be measured, and the inability to accurately distinguish measurement data due to spectral aliasing of multiple echo signals caused by the lack of signal isolation mechanism when a single host drives multiple probes.

[0006] To achieve the above objectives, the first aspect of the present invention provides a multi-channel synchronous length measurement system based on laser FMCW technology, comprising: The FMCW measurement host is used to generate frequency-modulated continuous wave laser signals. By utilizing the difference in optical path length set by multiple fiber channels, the effective bandwidth is divided into multiple frequency regions, and the echo signal is confined to the corresponding frequency region by using different fiber lengths. The pigtail is physically connected to the FMCW measurement host and is used as a transmission medium to export the continuous wave laser signal. The fiber optic beam splitter receives the continuous wave laser signal through the pigtail and distributes the energy of the continuous wave laser signal equally to multiple output channel ports. Multiple optical fiber channels are connected to the output channel ports of the optical fiber beam splitter, and have different optical path lengths, forming multiple independent optical signal transmission paths; Multiple optical lenses are positioned at the end of the optical fiber channel to focus laser signals onto the surface of the cable to be measured.

[0007] Furthermore, the FMCW measurement host integrates a narrow linewidth tunable laser, a function generator, and a temperature control circuit; the function generator is used to drive the narrow linewidth tunable laser to generate a highly linear sweep frequency signal, and the temperature control circuit is used to stabilize the operating wavelength of the narrow linewidth tunable laser.

[0008] Furthermore, the fiber beam splitter adopts a planar waveguide type optical splitter to ensure uniform optical power distribution among the multiple output channel ports; the multiple optical lenses each correspond to a cable of the length to be measured, and each optical lens independently focuses the laser onto the corresponding cable of the length to be measured.

[0009] Furthermore, the FMCW measurement host constructs a signal spectrum coordinate system, and detects the signal peak value when each optical fiber channel is stationary and the signal peak value when it is moving within the spectrum coordinate system. Based on the frequency difference between the frequency corresponding to the signal peak value when moving and the frequency corresponding to the signal peak value when stationary, the movement speed of the corresponding cable of the length to be measured is determined.

[0010] The second aspect of this invention provides a multi-channel synchronous length measurement method based on laser FMCW technology, applied to the multi-channel synchronous length measurement system based on laser FMCW technology described in the first aspect, comprising the following steps: The FMCW measurement host generates a frequency-modulated continuous wave laser signal, which is transmitted to the pigtail via an optical fiber network. The continuous wave laser signal from the pigtail is received by the fiber beam splitter and distributed to multiple fiber channels with different physical optical path lengths. The physical optical path lengths of the fiber channels are configured so that the echo signals of different channels can be converted to different frequency ranges. Multiple optical lenses emit modulated laser signals onto the surface of the cable to be measured and receive the laser echo signals reflected back from the cable. The FMCW measurement host receives the mixed laser echo signal reflected from the surface of the cable to be measured, and performs frequency mixing processing on the received mixed laser echo signal and the local oscillator light signal inside the FMCW measurement host. The FMCW measurement host performs spectrum analysis on the mixed signal. Based on the difference in optical path length of the multiple fiber optic channels, the full-band spectrum is divided into multiple independent frequency monitoring windows. The FMCW measurement host extracts the beat frequency information in each of the frequency monitoring windows, calculates the actual movement speed of the cable to be measured using the beat frequency information, and calculates the cumulative production length by integrating the actual movement speed over time.

[0011] Furthermore, the step of pre-setting multiple fiber optic channels specifically includes: adjusting the physical length of each fiber optic channel according to a preset reference beat frequency, so that the reference beat frequency is located at the center of a pre-divided frequency region, ensuring that when the cable of the length to be measured moves and causes a Doppler frequency shift, the signal spectrum peak of the fiber optic channel remains within the range of the corresponding frequency region.

[0012] Furthermore, in the step of emitting laser signals: the optical lens ensures that there is a fixed incident angle between the emission direction of the emitted laser center beam and the movement direction of the cable to be measured; the FMCW measurement host uses the fixed incident angle to construct a spatial geometric projection relationship, and calculates the actual movement speed of the cable to be measured based on the spatial geometric projection relationship.

[0013] Furthermore, after the FMCW measurement host performs spectral analysis on the mixed signal, the method further includes: the FMCW measurement host extracts the upper sweep beat frequency of each optical fiber channel during half a modulation period in which the laser frequency increases linearly with time, and the FMCW measurement host extracts the lower sweep beat frequency of each optical fiber channel during the other half modulation period in which the laser frequency decreases linearly with time.

[0014] Furthermore, the FMCW measurement host searches for and locks the frequency point with the largest signal amplitude within each frequency monitoring window, and determines the frequency corresponding to the frequency point as the upper and lower sweep frequency of each optical fiber channel. The difference information between the upper and lower sweep frequency is modulated using a triangular wave, and combined with the spatial geometric projection relationship, the actual movement speed of the cable of the length to be measured is calculated.

[0015] Furthermore, the calculation of the cumulative production length specifically includes: the FMCW measurement host uses the actual movement speed calculated within a single modulation cycle to calculate the single-step distance of the cable to be measured within a single modulation cycle; the FMCW measurement host discretely accumulates the continuously generated single-step distances during the full-time measurement process; and calculates the cumulative total length of the cable to be measured by statistically counting the total number of modulation cycles experienced during the measurement process.

[0016] This invention provides a multi-channel synchronous length measurement system and method based on laser FMCW technology. It has the following beneficial effects: 1. This invention utilizes an FMCW measurement host in conjunction with multiple fiber optic channels having predetermined optical path length differences. By leveraging these differences, the effective bandwidth of the FMCW measurement host is logically divided into multiple independent frequency regions. The FMCW measurement host maps the reflected echo signals from multiple cables of different lengths to be measured into non-overlapping frequency monitoring windows using the varying fiber lengths. Within a single scan cycle, the FMCW measurement host simultaneously calculates the motion state of multiple cables of different lengths. By employing the frequency division multiplexing principle, a single device can synchronously monitor multiple production lines, avoiding signal aliasing across multiple channels.

[0017] 2. This invention employs a triangular wave frequency modulation method in the FMCW measurement host. The FMCW measurement host extracts the upper and lower sweep frequency beat frequencies respectively, and uses the difference information between the upper and lower sweep frequency beat frequencies to eliminate the coupling effect of distance beat frequency on speed calculation, directly calculating the actual movement speed of the cable to be measured. By accumulating and integrating the displacement within a single modulation cycle, the FMCW measurement host realizes the conversion from instantaneous speed measurement to spatial length measurement, achieving non-contact synchronous measurement of both speed and length parameters.

[0018] 3. This invention implements differentiated optical path design for multiple optical fiber channels, adjusts the physical length of the optical fiber channels so that the reference beat frequency is located at the center of the pre-divided frequency region, and the FMCW measurement host reserves a frequency protection interval to accommodate the Doppler frequency shift caused by the movement of the cable to be measured. This ensures that the peak value of the echo signal spectrum always remains within the corresponding frequency monitoring window under the condition of high-speed movement of the cable to be measured. By using a frequency domain isolation mechanism based on optical path difference, signal crosstalk between adjacent optical fiber channels is prevented, ensuring the signal independence and data integrity of multi-channel parallel measurement. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the system architecture of the present invention; Figure 2 This is a schematic diagram illustrating the multi-channel signal spectrum principle of the present invention; Figure 3This is a schematic diagram of the FMCW triangular wave modulation waveform of the present invention; Figure 4 This is a schematic diagram of the beat frequency signal characteristics of the present invention; Figure 5 This is a schematic diagram of the method flow of the present invention.

[0020] The components include: 1. FMCW measurement host; 2. Pigtail; 3. Fiber optic bundle splitter; 4. Fiber optic channel; 5. Optical lens; and 6. Cable of the length to be measured. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] See attached document Figure 1 The present invention provides a multi-channel synchronous length measurement system based on laser FMCW technology, including an FMCW measurement host 1, a pigtail 2, an optical fiber beam splitter 3, multiple optical fiber channels 4, and multiple optical lenses 5.

[0023] The FMCW measurement host 1 serves as the laser source generation unit of the system. The FMCW measurement host 1 is configured to generate a continuous wave laser signal whose frequency varies with time and to modulate its frequency.

[0024] The FMCW measurement host 1 integrates a narrow-linewidth tunable laser (such as a DFB laser or an external cavity diode laser). This narrow-linewidth tunable laser has a long coherence length to support long-distance fiber optic transmission and measurement. The FMCW measurement host 1 also includes a high-precision function generator and temperature control circuitry. The function generator drives the laser to generate a highly linear sweep signal, while the temperature control circuitry stabilizes the laser's operating wavelength to prevent ambient temperature drift from affecting measurement accuracy. The output optical power of the narrow-linewidth tunable laser is set within a safe range for the human eye while simultaneously meeting the signal-to-noise ratio requirements after multi-channel beam splitting.

[0025] One end of the pigtail 2 is physically connected to the optical signal output interface of the FMCW measurement host 1. The pigtail 2 serves as a single-mode optical fiber transmission medium and is used to export the modulated laser signal generated by the FMCW measurement host 1 with low loss.

[0026] Fiber optic beam splitter 3 is equipped with a unique input channel port and a quantity of The output channel port of the fiber optic cable 2, with the end furthest from the FMCW measurement host 1, is physically connected to the input channel port of the fiber optic beam splitter 3. The continuous wave laser signal generated by the FMCW measurement host is transmitted in the fiber optic cable as a single laser beam, which is ultimately received by the fiber optic beam splitter and its energy is distributed to the output channel port of the fiber optic cable 3. Each output channel port enables the conversion from a single light source to multiple parallel measurement optical paths. The value is a positive integer greater than or equal to 2, representing the total number of measurement channels supported by the system. The fiber optic beam splitter 3 completes the conversion from a single light source to multiple parallel measurement optical paths.

[0027] The fiber optic beam splitter 3 preferably adopts a planar waveguide type (PLC) optical splitter to ensure... The uniformity of optical power distribution among the output channel ports is improved, reducing the loss difference between channels. The fiber optic connectors in pigtail 2 and fiber optic channel 4 are all polished using APC bevel grinding to reduce the interference of Fresnel reflection echoes from the fiber end face on the measurement system and improve the signal-to-noise ratio. Fiber optic channel 4 uses single-mode fiber to maintain the stability of the laser mode and prevent signal degradation caused by multimode dispersion.

[0028] Each output channel port of the fiber optic beam splitter 3 is independently connected to an optical lens 5 via a single optical fiber. Each output channel port extends outwards, forming An independent optical signal transmission path, The independent optical signal transmission paths spatially constitute multiple optical fiber channels.

[0029] Multiple fiber optic channels 4 are physically designed to have different optical path lengths, and the equivalent spatial optical path lengths corresponding to the multiple fiber optic channels 4 are respectively , This represents the optical path distance between each fiber optic channel 4 and the output of the fiber optic beam splitter 3 to the optical lens 5. This represents the total number of fiber optic channels 4.

[0030] The FMCW measurement host 1 utilizes the difference in optical path length between multiple fiber optic channels 4 to achieve channel isolation in the frequency domain. By using different fiber lengths, the echo signals reflected from multiple cables of varying lengths are confined to a specified frequency region for operation. Specifically, the effective bandwidth of the signal output by the FMCW measurement host 1 is divided into... A continuous frequency region, The number of regions is indicated by setting different optical path lengths. to This makes the first fiber optic channel 4 to the fourth The echo signals from each of the four fiber optic channels are mapped to different frequency regions, allowing the system to simultaneously detect multiple cables of varying lengths.

[0031] To prevent spectral aliasing between adjacent channels due to excessive Doppler frequency shift, in the division When operating in consecutive frequency regions, frequency protection intervals are reserved between adjacent regions. The bandwidth design of each frequency region not only considers the maximum possible Doppler frequency shift caused by the maximum possible movement speed of the cable of the specified length 6, but also the fundamental frequency fluctuation range caused by the fiber length tolerance, thereby ensuring that even under extreme operating conditions, the first... The signal peak value of each channel is still strictly limited to the [number]th [channel]. Within a logical frequency range.

[0032] When performing frequency detection, the FMCW measurement host 1 uses the difference in optical path length set between multiple fiber optic channels 4 to logically divide the effective bandwidth into... A series of consecutive frequency regions, each with a frequency range configured as follows: During data processing, frequency data is divided Peak finding is performed in each region to obtain N effective frequencies. By using different fiber lengths, the echo signals reflected by multiple targets under test are confined to the specified frequency region for operation. This allows the system to detect multiple target objects simultaneously, achieving accurate speed measurement of multiple targets. This achieves efficient measurement while reducing the cost of single-channel speed or length measurement.

[0033] Optical lens 5 is located at the end of optical fiber channel 4. Optical lens 5 is configured to spatially shape and focus the laser signal transmitted from optical fiber channel 4, converge the laser signal to the surface of cable 6 to be measured, and form a laser focusing point on cable 6 to be measured.

[0034] Multiple optical lenses 5 correspond to For each cable 6 to be measured in length, each optical lens 5 independently focuses a laser beam onto the corresponding cable 6. The first optical lens 5 corresponds to the first cable 6 to be measured in length, the second optical lens 5 corresponds to the second cable 6 to be measured in length, and so on, until the [number missing]th cable 6 is reached. The optical lens corresponds to the 5th... 6. Cable of length to be measured.

[0035] There is a fixed geometric relationship between the direction of the laser beam emitted from the center of the optical lens 5 and the direction of movement of the cable 6 whose length is to be measured, and the direction of the laser beam emitted from the center of the optical lens 5 forms an angle with the direction of movement of the cable 6 whose length is to be measured. .

[0036] The cable 6 to be measured is in motion, and the first cable 6 to be measured moves at a speed of... Running, the second cable of unknown length 6 moves at a speed Run until the first The length of the cable to be measured is 6 at the speed of movement. run, They represent the 1st to the 1st. The actual speed of movement of the cable 6 of the length to be measured.

[0037] The surface of the cable 6, to be measured, reflects or scatters the incident laser signal. The reflected laser signal, carrying Doppler frequency shift information, returns along the original optical path to the optical lens 5. Based on the FMCW velocity measurement principle, the reflected laser signal is detected, and the velocity is simultaneously measured. Velocity component of cable length 6 to be measured , They represent the 1st to the 1st. The velocity component of the cable 6 to be measured along the laser irradiation direction.

[0038] See attached document Figure 2 The FMCW measurement host 1 constructs a signal spectrum coordinate system. The vertical axis of the signal spectrum coordinate system is configured as the signal strength axis to represent the signal power intensity, and the horizontal axis of the signal spectrum coordinate system is configured as the FMCW signal frequency axis to represent the signal frequency value.

[0039] The FMCW measurement host 1 detects both stationary and moving signals within the operating frequency range of the first fiber optic channel 4. The stationary signal is represented on the spectrum by a frequency located at... The peak value of the solid line waveform at the point of motion indicates that the signal in motion is represented by a frequency at a frequency of [missing information] on the spectrum. The peak value of the dashed waveform at that point, and The frequency interval between them corresponds to the Doppler frequency shift generated by the first cable of the length to be measured 6, and the amount of Doppler frequency shift generated by the first cable of the length to be measured 6 is expressed as: , Indicates the stationary frequency of channel 1. Indicates the motion frequency of channel 1. This represents the velocity component of the first cable of length 6 to be measured. Indicates the laser wavelength.

[0040] Within the operating frequency range of the second fiber channel 4, the detected frequency is located at The peak value and frequency of the signal at rest are located at The peak value of the signal during motion at that location. Compared to The frequency offset is determined by the motion state of the second cable 6 to be measured, and the frequency offset generated by the second cable 6 to be measured is expressed as... , Indicates the stationary frequency of channel 2. Indicates the motion frequency of channel 2. This represents the velocity component of the second cable of length 6 to be measured. Indicates the laser wavelength.

[0041] And so on, FMCW measurement host 1 in the... Within the operating frequency range of each of the four fiber optic channels, the detected frequency is located at... The peak value and frequency of the signal at rest are located at The peak value of the signal during motion at that location. and The frequency difference between them directly reflects the first The speed of movement of the cable of length 6 to be measured, the first The frequency difference generated by the cable of length 6 to be measured is expressed as: , Indicates channel stationary frequency, Indicates channel Motion frequency, Indicates the first The velocity component of the cable of length 6 to be measured. Indicates the laser wavelength.

[0042] Specifically, the Doppler frequency shift caused by cable speed in each channel was calculated. And the actual speed of the cable. The relationship can be expressed by the following system of equations: ; in: The rest frequency, The frequency of motion.

[0043] See attached document Figure 3 The frequency modulation method performed by the FMCW measurement host 1 is not limited to triangular wave modulation, sawtooth wave modulation or sine wave modulation. Taking triangular wave modulation as an example, the FMCW measurement host 1 generates a local oscillator optical signal with a specific waveform. The frequency of the local oscillator optical signal shows a periodic change of linear increase and decrease with time. The change law of the local oscillator optical frequency is determined by the modulation period.

[0044] The operating frequency range of the FMCW measurement host 1 is defined by the starting frequency and the center frequency. The starting frequency represents the lowest frequency point of the sweep signal, and the center frequency represents the median frequency of the sweep signal.

[0045] The laser signal reflected back by the cable of length 6 forms a cable echo signal. The cable echo frequency lags behind the local oscillator frequency on the time axis, and the cable echo frequency shifts on the FMCW signal frequency axis compared to the local oscillator frequency.

[0046] The laser signal reflected by the cable 6 of the length to be measured returns to the FMCW measurement host 1. The FMCW measurement host 1 mixes the received cable echo signal with the local oscillator optical signal inside the FMCW measurement host 1. The mixing process is based on the coherent detection principle, and the difference frequency signal between the local oscillator optical signal frequency and the cable echo signal frequency is extracted by a photodetector.

[0047] Within the triangular wave modulation period generated by the FMCW measurement host 1, the laser frequency changes linearly with time. During the half-cycle of the laser frequency scanning upward, the local oscillator optical signal and the cable echo signal are mixed to generate the upward sweep frequency. During the other half-cycle of the laser frequency scanning downward, the local oscillator optical signal and the cable echo signal are mixed to generate the downward sweep frequency.

[0048] The movement of the cable 6 to be measured causes a Doppler frequency shift in the reflected laser. This Doppler frequency shift is superimposed on the distance beat frequency caused by the difference in optical path length, resulting in an asymmetry between the upper and lower sweep beat frequencies. The FMCW measurement host 1 calculates the subsequent speed and length based on the values ​​of the upper and lower sweep beat frequencies.

[0049] The cable 6 of the length to be measured moves in a straight line along the production line. The actual speed vector of the cable 6 of the length to be measured is distributed along the axial direction of the cable 6 of the length to be measured. The Doppler frequency shift carried by the echo signal received by the optical lens 5 reflects the velocity component of the cable 6 of the length to be measured in the direction of the laser beam optical axis.

[0050] A mathematical model is established between the actual velocity and the measured velocity components through geometric projection relationships. This model is then applied to the [specific context]. The mathematical model for the measurement channels is as follows: ; in: Indicates the first The velocity component along the laser irradiation direction detected by fiber optic channel 4; Indicates the first The actual speed of movement of the cable 6 of the length to be measured; This indicates the angle between the direction of the laser beam emitted from the center of the optical lens 5 and the direction of movement of the cable 6 of the length to be measured.

[0051] Using the aforementioned geometric model, the FMCW measurement host 1 restores the radial velocity component calculated from the Doppler frequency shift to the true linear velocity of the cable 6 to be measured, thereby ensuring the accuracy of the length measurement data.

[0052] See attached document Figure 4During the signal processing stage, the FMCW measurement host 1 acquires the upper and lower sweep beat frequencies within each modulation cycle, specifically for the first... With one fiber optic channel 4, the FMCW measurement host 1 identifies the upper and lower sweep frequency frequencies.

[0053] The movement of the cable of length 6 causes the reflected light signal to produce a Doppler effect. In the frequency domain, the Doppler effect manifests as a Doppler frequency shift. Based on the FMCW principle of triangular wave modulation, the Doppler frequency shift is obtained by calculating the absolute value of the difference between the upper and lower sweep beat frequencies. The following formula is used to calculate the... Doppler frequency shift corresponding to each of the four fiber optic channels: ; in: Indicates the first Doppler frequency shift of 4 fiber optic channels Indicates the first The upsweep frequency of fiber channel 4. Indicates the first The downsweep frequency of fiber channel 4.

[0054] There is a physical mapping relationship between the Doppler frequency shift and the radial velocity component of the cable 6 of the length to be measured in the laser irradiation direction. The physical mapping relationship is determined by the laser wavelength. The Doppler frequency shift is converted into the radial velocity component using the following formula: ; in: Indicates the first The radial velocity component of the cable 6 of the length to be measured along the laser irradiation direction, Indicates the first Doppler frequency shift of 4 fiber optic channels This indicates the wavelength of the laser emitted by the FMCW measurement host 1.

[0055] By utilizing the difference between the upper and lower sweep frequencies under triangular wave modulation and combining it with spatial geometric projection relationships, the actual speed of the cable 6 of the unknown length is calculated.

[0056] The following formula is used to calculate the first... The actual speed of movement of the cable 6 of the length to be measured: ; in: Indicates the first The actual speed of movement of the cable 6 of the length to be measured (i.e., the actual speed of movement of the cable). This indicates the wavelength of the laser emitted by the FMCW measurement host 1; Indicates the first The up-sweep frequency detected by fiber optic channel 4; Indicates the first The downsweep frequency detected by fiber optic channel 4.

[0057] The FMCW measurement host 1 eliminates the directional projection effect in the Doppler effect through the above formula. The denominator coefficient 4 in the formula comes from the superposition of the frequency difference and the two-times relationship of the Doppler frequency shift and the two-times relationship of the Doppler frequency shift and the velocity during the triangular wave modulation and demodulation process. The corrected linear velocity value is directly output using the actual motion velocity calculation formula, thus realizing the accurate quantification of the motion state of the cable 6 to be measured.

[0058] The FMCW measurement host 1 determines the direction of motion by comparing the numerical relationship between the upper and lower sweep frequencies. If the cable 6 to be measured moves away from the optical lens 5, the Doppler frequency shift is negative, resulting in one relationship; conversely, it results in another. The system has a direction flag. When the cable is detected to be moving backward, the calculated single-step distance will be marked as a negative value. When calculating the cumulative total length, the system performs an algebraic sum operation to automatically deduct the length generated by the backward movement, ensuring that the final output production length is the actual net length without the need for manual intervention to reset.

[0059] The frequency modulation of the FMCW measurement host 1 is set to have a fixed time reference, which is defined as the modulation period. Since the time span of the modulation period is short, the system regards the motion state of the cable 6 to be measured within a single modulation period as uniform linear motion.

[0060] Using the actual motion speed calculated within a single modulation cycle, the single-step distance of the cable 6 of the unknown length is calculated within a single modulation cycle. This is for the first... The formula for calculating the single-step distance for each fiber optic channel (4) is as follows: ; in: Indicates the first The single-step distance that the cable 6 to be measured moves within a single modulation cycle; Indicates the first The actual speed of movement of the cable 6 of the length to be measured; This indicates the modulation period of FMCW measurement host 1.

[0061] During the full-time measurement process, the FMCW measurement host 1 performs discrete accumulation and integration on the continuously generated single-step long distances. By statistically counting the total number of modulation cycles experienced during the measurement process, the cumulative total length of the cable 6 to be measured is calculated. The formula for calculating the cumulative total length is as follows: ; in: Indicates the first The cumulative total length of cable 6 to be measured during the measurement time; This indicates the total number of modulation cycles included in the measurement process; This represents the cyclic variable in a discrete-time series, representing the cyclic variable of the first time series. One modulation cycle; Indicates the first The first modulation period calculated The actual speed of movement of the cable 6 of the length to be measured; This indicates the modulation period of FMCW measurement host 1.

[0062] The above integral algorithm converts the measurement of instantaneous velocity value into the measurement of spatial length value, thereby realizing real-time monitoring of the production length of the cable 6 to be measured.

[0063] See attached document Figure 5 This invention provides a multi-channel synchronous length measurement method based on laser FMCW technology, comprising the following steps: S1. The FMCW host generates modulated lasers to set different optical path lengths for multiple channels: The FMCW measurement host 1 generates a frequency-modulated continuous wave laser signal and transmits it to the surface of the cable 6 to be measured via an optical fiber network. The laser frequency is periodically modulated using a triangular wave modulation method.

[0064] Multiple fiber optic channels 4 are pre-configured with different physical optical path lengths. The first fiber optic channel 4 is configured with an optical path length of... The second fiber channel 4 is configured with an optical path length of... Until the Each fiber optic channel has a configured optical path length of 4. Utilizing optical path length to The differences cause the echo signals from different channels to separate in the frequency domain.

[0065] Optical lenses 5 connected to the ends of multiple fiber optic channels 4 receive laser signals from the fiber optic channels 4. The optical lenses 5 focus the laser signals and project the focused laser spot onto the surface of the cable 6 of the length to be measured, which is in motion.

[0066] S2, Optical beam splitter distributes laser to perform initialization self-calibration and obtain zero-point reference: Fiber beam splitter 3 receives the modulated laser signal from pigtail 2 and distributes the modulated laser signal equally in power to multiple fiber channels 4. The multiple fiber channels 4 independently transmit the distributed laser signal.

[0067] Differentiated optical path length designs are implemented for multiple fiber channels 4, so that the first fiber channel 4 to the second fiber channel 4... Each fiber channel 4 has an increasing physical fiber length, and the difference in physical fiber length causes different time delays when the laser signal is transmitted in different fiber channels 4.

[0068] The magnitude of the time delay directly determines the reference beat frequency demodulated by the FMCW system, which is proportional to the frequency. Utilizing the principle of linear frequency modulation, the transmission time delay of the optical signal in the optical fiber is directly converted into the frequency difference of the mixing signal. By setting the fiber length, the static echo signal frequency of each fiber channel 4 is anchored at a specific position on the spectrum. Four fiber optic channels, the reference beat frequency is determined by the following formula: ; in: Indicates the first The reference beat frequency of each fiber optic channel 4 in a static state; This indicates the effective bandwidth of the signal from FMCW measurement host 1; Indicates the first The unidirectional optical path length set for each fiber optic channel 4; This indicates the speed of light propagation in the optical fiber medium; This indicates the modulation period of FMCW measurement host 1.

[0069] Based on the calculated reference beat frequency value, the physical length of each fiber channel 4 is adjusted independently. Specifically, this is achieved by precisely trimming the fiber length or connecting fiber delay lines in series, ensuring that the reference beat frequency of the fiber channel 4 is strictly within the pre-defined range. The center position of each frequency region is used as a reference to reserve the maximum bidirectional frequency tolerance for Doppler frequency shift caused by motion, ensuring that when the cable of length 6 undergoes high-speed motion causing positive or negative Doppler frequency shift, the first... The signal spectral peak of fiber channel 4 always remained at the [missing information]. Within the boundary range of each frequency region, this prevents cross-boundary movement and overlap with adjacent frequency regions, thus ensuring the accuracy of multi-channel parallel measurements.

[0070] Before officially starting the measurement of the cable 6 to be measured, the FMCW measurement host 1 executes an initialization self-calibration program. With the cable 6 to be measured in a completely stationary state, the FMCW measurement host 1 executes one or more complete frequency sweep cycles to obtain the actual stationary reference frequency of each fiber channel 4. The measured value may deviate from the theoretical calculation value due to the slight fluctuation of the refractive index caused by the change of fiber ambient temperature. The measured stationary reference frequency is stored in memory as the zero-point reference for subsequent calculations. During the dynamic measurement process, the frequency acquired in real time is differentially compared with the zero-point reference, thereby eliminating the influence of the slow drift of the fiber optical path due to the change of ambient temperature at the algorithm level and realizing zero-speed correction.

[0071] S3. Laser irradiation of moving cable generates Doppler frequency shift: Multiple optical lenses 5 emit modulated laser signals to the surface of the cable 6 to be measured and receive the laser signals reflected back from the surface of the cable 6. Since the cable 6 to be measured is in motion, the reflected laser signals generate a Doppler frequency shift relative to the emitted signals, and the echo signal returns along the original path.

[0072] The reflected laser signal, carrying frequency offset information, re-enters the optical lens 5. The reflected laser signal is transmitted in reverse along the fiber optic channel 4, passes through the fiber optic beam splitter 3, and finally returns to the receiving port of the FMCW measurement host 1.

[0073] The relationship between the moving speed of the cable 6 of the unknown length and the frequency change generated by the reflected laser signal follows the Doppler effect principle. The physical frequency change is determined by the following formula: ; in: This represents the frequency change of the reflected laser signal relative to the incident laser signal; This indicates the actual linear velocity of the cable 6 of the length to be measured; This represents the angle between the laser incident direction and the direction of movement of the cable 6 of the length to be measured; This indicates the center wavelength of the laser emitted by the FMCW measurement host 1.

[0074] S4. Receiving Echoes and Mixing to Extract Upper and Lower Scanning Frequencies: The FMCW measurement host 1 receives laser echo signals reflected from the surfaces of all cables 6 of the length to be measured via an optical fiber network. The received signal is physically a superposition of echoes from multiple channels. The internal photodetector mixes the received mixed laser echo signal with the local oscillator signal generated locally by the FMCW measurement host 1. Due to the pre-set differences in optical path lengths of different optical fiber channels 4, the laser echo signals of each channel experience different time delays, which are then converted into different reference beat frequencies falling within non-overlapping frequency ranges. This provides the physical basis for extracting independent signals from each channel and achieving frequency domain separation in subsequent spectrum analysis by dividing frequency monitoring windows. The FMCW measurement host 1 receives the combined laser echo signal from all channels, mixes it with the internal local oscillator signal, performs spectrum analysis, and divides the frequency range corresponding to the aforementioned optical path length differences into multiple independent frequency monitoring windows. Within each window, the independent echo signal of the corresponding channel is extracted, completing the frequency domain separation of the multi-channel signal. The mixing process is based on the principle of optical coherent detection and directly outputs an electrical signal containing multiple difference frequency information.

[0075] The electrical signal of the difference frequency information is then converted to current and voltage and amplified in the primary stage by a transimpedance amplifier, and then passed through an anti-aliasing low-pass filter to filter out high-frequency noise. The conditioned analog signal enters a high-speed analog-to-digital converter for digital sampling. The digital signal processor or field-programmable gate array inside the FMCW measurement host 1 performs a fast Fourier transform on the sampled digital sequence to convert the time domain signal into a frequency domain spectrum.

[0076] The FMCW measurement host 1 performs analog-to-digital conversion and spectrum analysis on the output electrical signal. Within half a modulation cycle in which the laser frequency emitted by the FMCW measurement host 1 increases linearly with time, the first... The upsweep beat frequency of fiber channel 4 is formed by the superposition of the frequency shift caused by distance and the frequency shift caused by velocity, and its mathematical expression is as follows: ; in: Indicates the first The upsweep beat frequency detected by fiber channel 4 during the laser frequency rise phase; Indicates by the first The distance beat frequency component caused by the time delay due to the optical path length of each fiber channel 4; This represents the Doppler frequency shift component generated by the movement speed of the cable 6 of the length to be measured.

[0077] During the other half of the modulation cycle in which the laser frequency emitted by FMCW measurement host 1 decreases linearly with time, the first... The downsweep beat frequency of fiber channel 4 is formed by the superposition of the frequency shift caused by distance and the frequency shift caused by velocity with different signs. Its mathematical expression is as follows: ; in: Indicates the first The down-sweep beat frequency detected by fiber channel 4 during the laser frequency decrease phase; Indicates by the first The distance beat frequency component caused by the time delay due to the optical path length of each fiber channel 4; This represents the Doppler frequency shift component generated by the movement speed of the cable 6 of the length to be measured.

[0078] Through step S4 above, the original frequency data required for subsequent velocity calculation and length integration is obtained completely.

[0079] S5. Spectrum Partitioning Peak Finding and Calculation Speed ​​and Cumulative Length: The FMCW measurement host 1 performs spectrum analysis on the digital signal after analog-to-digital conversion. Based on the pre-set optical path differences of multiple fiber optic channels 4, the entire frequency band spectrum is divided into... A separate frequency monitoring window. In the... Within each frequency monitoring window, the system executes a peak-finding algorithm to search for the spectral peak with the largest signal amplitude, and directly determines the frequency coordinate value corresponding to that spectral peak as the [number]th frequency monitoring window. The up-sweep beat frequency (during the rising half-cycle) or the down-sweep beat frequency (during the falling half-cycle) of each fiber channel 4.

[0080] In the specific spectrum extraction process, in order to improve the resolution and accuracy of frequency detection, the FMCW measurement host 1 is not limited to directly reading the discrete maximum points after FFT transformation. Instead, it uses the centroid method or Gaussian fitting algorithm to perform sub-pixel level interpolation on the main peak of the spectrum, selects the maximum peak point and multiple frequency points to its left and right, and calculates the precise center frequency of the spectral peak based on the energy distribution. This breaks through the limitation of FFT frequency resolution, making the accuracy of the obtained upper and lower sweep beat frequencies better than one frequency step of FFT, thus improving the accuracy of subsequent speed calculation. To prevent noise interference, the system has a preset signal-to-noise ratio threshold. Only when the extracted peak signal intensity is higher than the background noise floor by a certain number of decibels is it determined to be a valid echo signal; otherwise, it is considered invalid or packet loss is processed to prevent false signals from interfering with the length measurement results.

[0081] Solving the first... using the Doppler frequency shift principle and spatial geometric projection relationship Based on the actual movement speed of the cable 6 to be measured, the FMCW measuring host 1 calculates the accumulated production length by integrating the speed over time, thus achieving parallel output of speed and length parameters of multiple cables 6 to be measured in a single measurement cycle.

[0082] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A multi-channel synchronous length measurement system based on laser FMCW technology, characterized in that, include: The FMCW measurement host (1) is used to generate frequency-modulated continuous wave laser signals. By using the optical path length difference set by multiple optical fiber channels (4), the effective bandwidth of the frequency-modulated continuous wave laser signal is divided into multiple frequency regions. The echo signal is limited to the corresponding frequency region by using different optical fiber lengths. The pigtail (2) is physically connected to the FMCW measurement host (1) and is used as a transmission medium to export the continuous wave laser signal; The fiber optic beam splitter (3) receives the continuous wave laser signal through the pigtail (2) and distributes the energy of the continuous wave laser signal equally to multiple output channel ports. Multiple optical fiber channels (4) are connected to the output channel port of the optical fiber beam splitter (3), and each optical fiber channel (4) has a different optical path length, forming multiple independent optical signal transmission paths; Multiple optical lenses (5) are disposed at the end of the optical fiber channel (4) to focus the continuous wave laser signal onto the surface of the cable (6) to be measured in length.

2. The multi-channel synchronous length measurement system based on laser FMCW technology according to claim 1, characterized in that, The FMCW measurement host (1) integrates a narrow linewidth tunable laser, a function generator and a temperature control circuit. The function generator is used to drive the narrow linewidth tunable laser to generate a highly linear sweep signal, and the temperature control circuit is used to stabilize the operating wavelength of the narrow linewidth tunable laser.

3. The multi-channel synchronous length measurement system based on laser FMCW technology according to claim 1, characterized in that, The fiber beam splitter (3) adopts a planar waveguide type optical splitter to ensure uniform optical power distribution among multiple output channel ports; Each of the plurality of optical lenses (5) corresponds to a cable (6) of length to be measured, and each optical lens (5) independently focuses the laser onto the corresponding cable (6) of length to be measured.

4. The multi-channel synchronous length measurement system based on laser FMCW technology according to claim 1, characterized in that, The FMCW measurement host (1) constructs a signal spectrum coordinate system, and detects the signal peak value when each optical fiber channel (4) is stationary and the signal peak value when it is moving in the spectrum coordinate system. Based on the frequency difference between the frequency corresponding to the signal peak value when it is moving and the frequency corresponding to the signal peak value when it is stationary, the movement speed of the corresponding cable (6) of the length to be measured is determined.

5. A multi-channel synchronous length measurement method based on laser FMCW technology, characterized in that, The multi-channel synchronous length measurement system based on laser FMCW technology described in claims 1-4 includes the following steps: The FMCW measurement host (1) generates a frequency-modulated continuous wave laser signal, which is transmitted to the pigtail (2) via an optical fiber network. The continuous wave laser signal is received from the pigtail (2) by the fiber beam splitter (3) and distributed to multiple fiber channels (4) with different physical optical path lengths. Multiple optical lenses (5) emit modulated laser signals onto the surface of the cable (6) whose length is to be measured, and receive the laser echo signals reflected back by the cable (6) whose length is to be measured; The FMCW measurement host (1) receives the laser echo signal reflected from the surface of the cable (6) to be measured, and performs frequency mixing processing on the received laser echo signal and the local oscillator light signal inside the FMCW measurement host (1); The FMCW measurement host (1) performs spectrum analysis on the signal after mixing. Based on the difference in optical path length of the multiple fiber channels (4) set in advance, the full-band spectrum is divided into multiple independent frequency monitoring windows. The FMCW measurement host (1) extracts the beat frequency information in each of the frequency monitoring windows, calculates the actual movement speed of the cable (6) to be measured through the beat frequency information, and calculates the cumulative production length by calculating the actual movement speed.

6. The multi-channel synchronous length measurement method based on laser FMCW technology according to claim 5, characterized in that, The step of pre-setting multiple fiber optic channels (4) specifically includes: Based on the preset reference beat frequency, the optical path length of each optical fiber channel (4) is adjusted so that the reference beat frequency is located at the center of the pre-divided frequency region, ensuring that when the Doppler frequency shift is caused by the movement of the cable (6) of the length to be measured, the signal spectrum peak of the optical fiber channel (4) remains within the range of the corresponding frequency region.

7. The multi-channel synchronous length measurement method based on laser FMCW technology according to claim 5, characterized in that, In the step of emitting the laser signal: The optical lens (5) makes a fixed incident angle between the emitted laser center light and the movement direction of the cable (6) whose length is to be measured. The FMCW measurement host (1) constructs a spatial geometric projection relationship based on the incident angle and calculates the actual movement speed of the cable (6) whose length is to be measured based on the spatial geometric projection relationship.

8. The multi-channel synchronous length measurement method based on laser FMCW technology according to claim 5, characterized in that, After the FMCW measurement host (1) performs spectrum analysis on the mixed signal, it further includes: The FMCW measurement host (1) extracts the up-sweep frequency of each of the fiber channels (4) within half a modulation period during which the laser frequency increases linearly with time. The FMCW measurement host (1) extracts the down-sweep frequency of each of the fiber channels (4) during the other half of the modulation period when the laser frequency decreases linearly with time.

9. The multi-channel synchronous length measurement method based on laser FMCW technology according to claim 8, characterized in that, The extraction of the upper and lower sweep frequency of each of the optical fiber channels (4) specifically includes: The FMCW measurement host (1) extracts the frequency point with the largest signal amplitude in each frequency monitoring window, determines the upper and lower sweep frequency of each fiber channel (4), uses triangular wave modulation of the difference information between the upper and lower sweep frequency, and combines the spatial geometric projection relationship to calculate the actual movement speed of the cable (6) of the length to be measured.

10. The multi-channel synchronous length measurement method based on laser FMCW technology according to claim 9, characterized in that, The calculation of cumulative production length specifically includes: The FMCW measurement host (1) uses the actual motion speed calculated in a single modulation cycle to calculate the single step distance of the cable (6) to be measured in a single modulation cycle. During the full-time measurement process, the FMCW measurement host (1) discretely accumulates the continuously generated single step distances and calculates the cumulative total length of the cable (6) to be measured by statistically analyzing the total number of modulation cycles experienced during the measurement process.

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