A laser Doppler train speed measuring device supporting step-by-step independent adjustment of working depth of field and working distance

Abstract

This invention relates to the field of train speed measurement technology, and discloses a laser Doppler train speed measuring device that supports independent step-by-step adjustment of working depth of field and working distance. The device includes a light source module, an optical module, and a processor. The optical module has a slide rail unit and two fiber optic collimators symmetrically arranged on both sides of the central axis of the slide rail unit, supporting independent step-by-step adjustment modes: Mode I adjusts the working depth of field by changing the convergence angle of the detection laser on the rail surface by adjusting the angle of the two fiber optic collimators; Mode II adjusts the working distance by adjusting the distance between the two fiber optic collimators using the slide rail unit. This invention enables decoupled independent setting of working depth of field and working distance, and can flexibly adapt to different system requirements; by simplifying the optical structure, it reduces instability factors in vibration environments, improves the echo signal-to-noise ratio and speed measurement robustness; and it supports adaptive closed-loop adjustment of the working distance, ensuring the reliability of speed measurement under strong vibration conditions.

Description

Technical Field

[0001] This invention relates to the field of train speed measurement technology, and in particular to a laser Doppler train speed measuring device that supports independent step-by-step adjustment of working depth of field and working distance. Background Technology

[0002] The rapid development of high-speed rail networks has greatly promoted cooperation between cities, driven regional economic integration, shortened spatial and temporal distances, and made the flow of people and goods more efficient and convenient. However, with the continuous increase in train speeds, more stringent requirements are being placed on the accuracy, reliability, and environmental adaptability of speed measurement systems.

[0003] Currently, train speed measurement methods mainly include wheel-axle speed sensors, microwave Doppler radar, accelerometers, and satellite navigation systems. Wheel-axle speed sensors are technologically mature and relatively inexpensive, but they are prone to measurement errors when the wheel slips or spins freely on the rails. Microwave Doppler radar is a non-contact measurement method with high reliability, but its Doppler frequency shift is small when the train is running at low speeds, resulting in low speed measurement accuracy. Accelerometers obtain speed through integration, and their accumulated errors become significant after long-term operation. While satellite navigation systems can provide absolute position and speed information, they may fail to measure speed in environments with signal obstruction, such as tunnels and mountainous areas. For a wide speed measurement range covering 0–700 km / h for rail trains, all of the above methods have certain limitations and cannot simultaneously achieve high accuracy and high reliability under all operating conditions.

[0004] Against this backdrop, laser Doppler velocimetry technology, with its advantages of non-contact measurement, strong anti-interference capability, and immunity to wheel-rail slippage, is becoming an important development direction in the field of high-speed rail speed measurement. This technology uses a laser beam to illuminate the rail surface and utilizes the Doppler effect information carried in the echo signal to obtain the real-time speed of the train. It has the potential for full-speed-range, high-precision measurement, providing technical support for safer and smarter high-speed railway operation. In practical applications, when installing a laser Doppler velocimetry device under the train, its laser beam must illuminate the rail surface, and the echo signal must be received by a detector. Considering the different working distance requirements for speed measuring devices in different types of rail transit trains: for wheel-rail trains, due to the larger space between the train bottom and the rail, a longer working distance is required for the speed measuring device; while for maglev trains, the levitation gap is smaller, and the distance between the speed measuring device and the track is shorter, thus requiring a shorter working distance. However, currently available laser Doppler velocimetry products (such as the ProSpeed ​​series from Polytec in Germany and the InteliSENS series from Ptoton in the UK) all adopt a fixed working distance design. To adapt to different working distance requirements, different product models must be selected, resulting in insufficient flexibility and difficulty in meeting the adaptation needs of special working distances. Furthermore, most existing products are designed for target speed measurement in stable environments, such as length and speed measurements in manufacturing processes like rolling, textiles, film, and paper production in factories to achieve precise dimensional control. However, in train speed measurement applications, train operation involves significant vibrations, and existing speed measurement products cannot guarantee robustness in such dynamic environments.

[0005] In summary, current laser Doppler velocimetry products on the market cannot simultaneously meet the speed measurement requirements of different types of railway trains. Furthermore, the adjustment of the working distance and depth of field are coupled, preventing independent control. Additionally, the introduction of extra optical components reduces the robustness of the system's detection to some extent. Therefore, a new laser Doppler train speed measurement solution is urgently needed. Summary of the Invention

[0006] This invention provides a laser Doppler train speed measuring device that supports independent step-by-step adjustment of working depth of field and working distance, in order to overcome the shortcomings of the prior art.

[0007] This invention provides a laser Doppler train speed measuring device that supports independent step-by-step adjustment of working depth of field and working distance, comprising: The light source module is used to emit a first probe light and a second probe light with a set wavelength; An optical module is used to receive the first and second detection beams. Through train speed measurement, it receives beat frequency signals containing Doppler frequency shift information scattered back from the rail surface by the first and second detection beams. The optical module includes a slide rail unit, a first fiber optic collimator for receiving the first detection beam, and a second fiber optic collimator for receiving the second detection beam. The first and second fiber optic collimators are symmetrically arranged on both sides of the midpoint of the slide rail unit and can move synchronously towards or away from each other. The optical module supports step-by-step independent adjustment modes: Mode I: Adjusting the angle between the first and second detection beams on the rail surface by adjusting the angle of the first and second fiber optic collimators to adjust the working depth of field; Mode II: Adjusting the distance between the first and second fiber optic collimators using the slide rail unit to adjust the working distance. The processor is used to receive the beat frequency signal and calculate the train speed measurement information.

[0008] According to the present invention, a laser Doppler train speed measuring device that supports step-by-step independent adjustment of working depth of field and working distance is provided. The working depth of field is defined as the difference between the maximum working distance and the minimum working distance at which the laser Doppler train speed measuring device can achieve effective speed measurement.

[0009] According to the present invention, a laser Doppler train speed measuring device that supports independent step-by-step adjustment of working depth of field and working distance is provided. The light source module includes a narrow linewidth continuous laser and a 1-to-2 fiber beam splitter. The narrow linewidth continuous laser is used to emit a narrow linewidth detection laser beam of a set wavelength, and the 1-to-2 fiber beam splitter is used to split the narrow linewidth detection laser beam into a first detection beam and a second detection beam.

[0010] According to the present invention, a laser Doppler train speed measuring device that supports independent step-by-step adjustment of working depth of field and working distance is provided. The optical module further includes a first adjustment auxiliary platform and a second adjustment auxiliary platform. The first adjustment auxiliary platform and the second adjustment auxiliary platform are symmetrically arranged on both sides of the midpoint of the slide rail unit and can perform synchronous movements in opposite directions or back directions. The first fiber collimator is fixed on the first adjustment auxiliary platform and the second fiber collimator is fixed on the second adjustment auxiliary platform.

[0011] According to the present invention, a laser Doppler train speed measuring device that supports independent step-by-step adjustment of working depth of field and working distance is provided. The first adjustment auxiliary platform and the second adjustment auxiliary platform are respectively provided with angle scale markings to assist in reading the convergence angle of the first detection light and the second detection light on the rail surface.

[0012] According to the present invention, a laser Doppler train speed measuring device that supports independent step-by-step adjustment of working depth of field and working distance is provided. The slide rail unit is provided with distance scale markings to assist in adjusting the distance between the first adjustment auxiliary platform and the second adjustment auxiliary platform.

[0013] According to the present invention, a laser Doppler train speed measuring device that supports independent step-by-step adjustment of working depth of field and working distance is provided. The optical module further includes an acousto-optic modulator and an acousto-optic modulator driver. The acousto-optic modulator is used to introduce a set initial frequency to the beat frequency signal generated by the convergence of the first and second probe lights on the rail surface. The acousto-optic modulator driver is used to provide a high-frequency electrical signal to the acousto-optic modulator.

[0014] According to the present invention, a laser Doppler train speed measuring device that supports independent step-by-step adjustment of working depth of field and working distance is provided. The optical module further includes a converging lens and a photodetector. The converging lens is disposed at the midpoint of the slide rail unit. The converging lens is used to receive the backscattered light when the first and second probe lights are scattered on the rail surface, and couples the backscattered light into the photodetector for photoelectric conversion to obtain a beat frequency signal.

[0015] The laser Doppler train speed measuring device according to the present invention, which supports step-by-step independent adjustment of working depth of field and working distance, further includes a power supply module for supplying power to the light source module, the optical module and the processor.

[0016] This invention also provides a laser Doppler train speed measurement method, comprising: The laser Doppler train speed measuring device that supports independent adjustment of working depth of field and working distance as described above is installed on the bottom of the train to be measured, and the first detection light and the second detection light are used to illuminate the surface of the rail. The train under test is operated, and the train speed is measured using the laser Doppler train speed measuring device to obtain the train speed information of the train under test, wherein the train speed information includes speed and direction.

[0017] The laser Doppler train speed measuring device provided by this invention, which supports independent step-by-step adjustment of working depth of field and working distance, can bring at least the following beneficial effects: In Mode I, the convergence angle of the first and second fiber optic collimators on the rail surface is changed by adjusting the angles of the first and second probe beams, thus independently setting the working depth of field. In Mode II, the sliding rail unit is used to make the first and second fiber optic collimators move synchronously in opposite directions or back to back, independently adjusting the working distance. These two adjustment stages are independent and do not interfere with each other, allowing the speed measuring device to flexibly adapt to different rail transit systems, from wheel-rail trains to maglev trains, without the need to replace different models of products, greatly improving the versatility and engineering adaptability of the speed measuring device.

[0018] This invention directly controls the working depth of field through angle adjustment, achieving flexible depth-of-field setting without the need for additional plano-concave lenses or other complex optical components. This simplified optical design effectively reduces the number of optical components, mitigating potential instability factors such as loosening, displacement, or coupling misalignment of optical components caused by long-term vibration. This makes the overall structure of the speed measuring device more compact and robust, better adapting to the strong vibration conditions of high-speed train operation. Secondly, it avoids the absorption and divergence of the probe beam energy by redundant optical components, allowing more scattered light carrying Doppler frequency shift information to be effectively received. This significantly improves the signal-to-noise ratio of the echo signal and the speed measurement accuracy across the entire speed range, ensuring that the speed measuring device can still output stable and reliable train speed measurement information in complex track sections such as turnouts and rail gaps.

[0019] This invention features angle scale markings on the adjustment auxiliary platform and distance scale markings on the slide rail unit. This allows on-site engineers to quickly and accurately set the working depth of field and working distance step by step according to the actual vehicle type (wheel-rail or maglev) and track conditions. This user-friendly design lowers the debugging threshold of the speed measuring device and ensures rapid deployment capability under "large speed measuring range and all working conditions". Attached Figure Description

[0020] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the internal structure of a laser Doppler train speed measuring device that supports independent step-by-step adjustment of working depth of field and working distance, provided in an embodiment of the present invention. Figure 2 A schematic diagram of a slide rail unit, a first adjustment auxiliary platform, and a second adjustment auxiliary platform for a laser Doppler train speed measuring device that supports independent step-by-step adjustment of working depth of field and working distance, provided for an embodiment of the present invention; Figure 3 This is a schematic diagram illustrating the working depth of field adjustment of a laser Doppler train speed measuring device that supports independent step-by-step adjustment of working depth of field and working distance, provided by an embodiment of the present invention. Figure 4 This is a schematic diagram illustrating the working distance adjustment of a laser Doppler train speed measuring device that supports independent step-by-step adjustment of working depth of field and working distance, as provided in an embodiment of the present invention.

[0022] Reference numerals: 100, Light source module; 200, Optical module; 300, Circuit module; 1, Narrow linewidth continuous laser; 2, 1-to-2 fiber optic beam splitter; 3, First fiber optic collimator; 4, Second fiber optic collimator; 5, Acousto-optic modulator; 6, Acousto-optic modulator driver; 7, Converging lens; 8, Photodetector; 9, Motorized slide rail unit; 10, Power supply module (power circuit board); 11, Processor (signal circuit board); 12, Rail. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, embodiments of this invention, and should not be construed as limiting the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. In the description of this invention, it should be understood that the terminology used is for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0024] The present invention provides a laser Doppler train speed measuring device that supports independent step-by-step adjustment of working depth of field and working distance, which may include: The light source module includes a narrow linewidth continuous laser and a 1-to-2 fiber beam splitter. The narrow linewidth continuous laser is used to emit a narrow linewidth probe laser beam of a set wavelength (e.g., a continuous laser of 1550 nm). The 1-to-2 fiber beam splitter is used to split the narrow linewidth probe laser beam into a first probe beam and a second probe beam.

[0025] The optical module is used to receive the first and second detection beams and, through train speed measurement, receive the beat frequency signal containing Doppler frequency shift information scattered back from the rail surface by the first and second detection beams. The optical module includes a slide rail unit (preferably an electrically powered slide rail unit), a first adjustment auxiliary platform, a second adjustment auxiliary platform, a first fiber collimator for receiving the first probe light, and a second fiber collimator for receiving the second probe light. The first and second adjustment auxiliary platforms are symmetrically arranged on both sides of the midpoint of the slide rail unit and are capable of synchronous movement towards or away from each other (synchronous movement can be controlled by a circuit). The first fiber collimator is fixed to the first adjustment auxiliary platform, and the second fiber collimator is fixed to the second adjustment auxiliary platform (it can be fixed through mounting holes). The optical module supports step-by-step independent adjustment modes: Mode I: By adjusting the angles of the first and second probe beams on the rail surface, the working depth of field can be adjusted by adjusting the first and second adjustment auxiliary platforms (i.e., the angles of the first and second fiber collimators); Mode II: The working distance can be adjusted by using the slide rail unit to adjust the distance between the first and second adjustment auxiliary platforms (i.e., the distance between the first and second fiber collimators). The first adjustment auxiliary platform and the second adjustment auxiliary platform are respectively provided with angle scale marks to assist in reading the convergence angle of the first detection light and the second detection light on the rail surface; the slide rail unit is provided with distance scale marks to assist in adjusting the distance between the first adjustment auxiliary platform and the second adjustment auxiliary platform. The optical module further includes an acousto-optic modulator and an acousto-optic modulator driver. The acousto-optic modulator is used to introduce a set initial frequency to the beat frequency signal generated by the convergence of the first and second detection beams on the rail surface, so as to eliminate spectral aliasing caused by the direction of train movement, thereby enabling the speed measuring device to determine the direction of train movement. The acousto-optic modulator driver is used to provide a high-frequency electrical signal to the acousto-optic crystal of the acousto-optic modulator, so as to drive the generation of a sound field inside the crystal, thereby realizing rapid control of the laser beam. The optical module further includes a converging lens and a photodetector. The converging lens is located at the midpoint of the slide rail unit. The converging lens is used to receive the backscattered light when the first and second probe lights are scattered on the rail surface, and couples the backscattered light into the photodetector for photoelectric conversion to obtain a beat frequency signal.

[0026] The processor is used to receive the beat frequency signal and calculate the train speed measurement information. Specifically, the processor is used to perform the following functions: set the output power of the narrow linewidth continuous laser; provide the required 10MHz reference signal to the acousto-optic modulator driver; set the distance between the two adjustment auxiliary platforms on the slide rail; collect and process the photoelectric conversion signal output by the photodetector; and upload the calculated speed data to the host computer software.

[0027] The power supply module is used to supply power to the light source module, the optical module, and the processor. Specifically, it is used to convert the externally input 110V DC voltage, and its output includes: 12V voltage for powering the narrow linewidth continuous laser, the photodetector, the slide rail unit, and the processor; 24V voltage for powering the acousto-optic modulator driver; and 4V voltage for the modulation signal input of the acousto-optic modulator driver.

[0028] The following is combined Figure 1 , Figure 2 , Figure 3 and Figure 4 The working process of a laser Doppler train speed measuring device that supports independent step-by-step adjustment of working depth of field and working distance provided in this embodiment is described in detail.

[0029] refer to Figure 1When the laser Doppler train speed measuring device is in operation, it is installed at the bottom of the train. During installation, it is essential to ensure that the converging lens 7 remains parallel to the rail surface. A narrow-linewidth continuous laser 1 emits a continuous laser beam with a wavelength of 1550 nm, which is split into two beams by a 50:50 splitting fiber beam splitter 2. The first probe beam is connected to a first fiber collimator 3 and, after collimation, directly incident on the surface of the rail 12. The second probe beam undergoes frequency shifting processing via an acousto-optic modulator 5 before being connected to a second fiber collimator 4. After collimation, the second probe beam illuminates the surface of the rail 12 and converges with the first probe beam on the rail 12 surface, thereby generating a beat frequency signal. The acousto-optic modulator 5 is used to apply a fixed initial frequency to the beat frequency signal to eliminate spectral aliasing caused by the train's direction of motion, enabling the laser Doppler speed measuring device to determine the train's direction of travel. The acousto-optic modulator driver 6 provides a high-frequency electrical signal to the acousto-optic crystal in the acousto-optic modulator 5 to drive the formation of an acoustic field inside the crystal, thereby achieving rapid frequency modulation of the laser beam. The first fiber collimator 3 and the second fiber collimator 4 are respectively fixed to two adjustment auxiliary platforms attached to the electric slide rail unit 9, used to adjust the measurement half-angle α between the two probe beams, thereby achieving independent adjustment of the working depth of field of the laser Doppler train speed measuring device. The two adjustment auxiliary platforms are symmetrically arranged about the central axis of the electric slide rail unit 9. Through circuit control, the two adjustment auxiliary platforms can be synchronously moved closer to or further away from the central axis. Each adjustment auxiliary platform has a mounting hole at its center for fixing the fiber collimator. By adjusting the position of the auxiliary platforms on the electric slide rail unit 9, the working distance of the laser Doppler train speed measuring device can be independently adjusted. After completing the adjustment of the working depth of field and working distance, both adjustment auxiliary platforms and the electric slide rail unit 9 are locked by a set screw structure to prevent changes in the adjustment parameters due to vibration during train operation. The backscattered light corresponding to the beat frequency signal is received by the converging lens 7 and finally coupled to the photosensitive surface of the photodetector 8 to complete the photoelectric conversion. Subsequently, the processor 11 collects and processes the output signal of the photodetector 8 to obtain information such as the train's running speed, running direction, and distance, and uploads the calculation results to the host computer. The processor 11 is also used to set the output power of the narrow linewidth continuous laser 1, provide the required 10 MHz reference signal for the acousto-optic modulator driver 6, and control the electric slide rail unit 9 to set the distance d between the two adjustment auxiliary platforms. The power supply module 10 is used to convert the external 110V DC input voltage, and its output includes: 12V DC voltage for powering the narrow linewidth continuous laser 1, photodetector 8, electric slide rail unit 9, and signal circuit board 11; 24V DC voltage for powering the acousto-optic modulator driver 6; and 4V voltage for the modulation signal input of the acousto-optic modulator driver 6.

[0030] According to the reference Figure 1 The diagram shown is an internal structure schematic of a laser Doppler train speed measuring device that supports independent step-by-step adjustment of working depth of field and working distance, according to an embodiment of the present invention. The relationship between Doppler frequency shift and train speed is expressed as follows:

[0031] In the formula, f Dop The laser Doppler frequency shift is the beat frequency signal acquired by the photodetector 8. f M With the initial frequency shift provided by the acousto-optic modulator 5 f aom The calculation shows that the system measures half of the included angle. α The angle between the first or second probe beam and the perpendicular normal direction of the train track 12 (i.e., the backscattering direction) is defined as the angle between the probe beam and the backscattering direction. The working wavelength λ is the emitted laser wavelength λ of the narrow-linewidth continuous laser 1. After installing the laser Doppler velocimetry device and adjusting the working depth of field and working distance, the device measures the half-angle. α Laser operating wavelength λ and initial frequency shift f aom All of these are known quantities, meaning they can be obtained from the beat frequency signal acquired by the photodetector 8. f M Laser Doppler frequency shift information was calculated. f Dop In order to obtain the train's operating speed. v .

[0032] After obtaining train speed information, the train's travel distance can be obtained simultaneously by integrating the speed. Furthermore, this can be combined with the beat frequency signal. f M With initial frequency shift f aom It can determine the direction of train travel. For example, when the laser wavelength λ in the laser Doppler train speed measuring device is set to 1550nm, it measures the half-angle. α The initial frequency shift is 7°. f aom When the frequency is 80MHz, if the beat frequency signal acquired by the photodetector is... f M If the MHz frequency is 90, the train's speed can be calculated as 228.934 km / h using the above formula. If the train maintains this speed for 20 seconds, the distance traveled is 1271.854 m. If preset... f M - f aom >0 is the positive direction. fM - f aom If <0 indicates a negative direction, then the train's direction of travel can be determined to be positive based on the beat frequency information obtained from the photoelectric detector.

[0033] The electric slide rail unit 9 designed in the light source module 200 of the present invention has the following advantages: (1) It enables the laser Doppler train speed measuring device to support step-by-step adjustment mode: the working depth of field is determined by angle adjustment in the first stage, and the working distance is determined by adjusting the distance between the two fiber collimators by the slide rail assembly in the second stage. The above two stages of adjustment are independent of each other, thereby realizing the decoupling setting of working depth of field and working distance. (2) This design eliminates the need to add a plano-concave cylindrical lens after the fiber collimator in the optical system. The working depth of field can be adjusted by the angle adjustment auxiliary module on the electric slide rail unit 9, thereby reducing the number of optical devices and reducing the unstable factors that may be introduced during the optical coupling process. At the same time, avoiding the use of plano-concave cylindrical lenses can prevent the energy of the probe beam from diverging and avoid the energy of the echo signal from decreasing, thereby improving the system signal-to-noise ratio and speed measurement accuracy. (3) The electric slide rail unit 9 also has a closed-loop feedback control function. When the speed measurement is abnormal or the speed calculation fails, the working distance can be adaptively adjusted so that the measured rail can re-enter the effective working depth range, thereby further improving the stability and reliability of the speed measuring device under strong vibration conditions.

[0034] refer to Figure 2 The figure shows a schematic diagram of the electric slide rail unit 9 of a laser Doppler train speed measuring device that supports independent step-by-step adjustment of working depth of field and working distance, according to an embodiment of the present invention. Two adjustment auxiliary platform modules are provided on the electric slide rail unit 9. Each adjustment auxiliary platform module has a mounting hole at its center for fixing the fiber optic collimator. The two adjustment auxiliary platform modules are symmetrically arranged about the central axis of the electric slide rail unit 9 and achieve synchronous movement towards or away from the central axis through a reverse-designed lead screw thread structure. Precision scale lines are provided at the edge of the electric slide rail unit 9 to obtain the actual distance d between the center positions of the two adjustment auxiliary platforms, thereby facilitating precise adjustment of the working distance. Simultaneously, scale markings are also provided on the adjustment auxiliary platforms to read the specific value of the half-angle α measured by the speed measuring device system after the working depth of field adjustment is completed. The electric slide rail unit 9 is powered by a 12V DC power supply and can communicate with a host computer via a serial port for remote control. Furthermore, the electric slide rail unit 9 has a closed-loop feedback control function, which can achieve adaptive adjustment of the working distance in case of speed measurement abnormalities or speed calculation failures. In addition, both the adjustment auxiliary platform and the electric slide rail unit 9 are equipped with a top screw locking structure, which is used to reliably lock the structure after the working depth of field and working distance are adjusted, so as to prevent the structure from loosening due to vibration during train operation, thereby affecting the accuracy of speed calculation.

[0035] refer to Figure 3 The figure shows a schematic diagram of the working depth of field adjustment of a laser Doppler train speed measuring device that supports independent step-by-step adjustment of working depth of field and working distance, according to an embodiment of the present invention. Within the convergence area of ​​the two detection beams, the solid line represents the optimal speed measuring position where the detection light energy is most concentrated; the upper and lower dashed lines define the effective area where the two detection beams can converge, i.e., the working depth of field of the laser Doppler speed measuring device. The vertical vibrations of a train during operation will cause a vertical displacement of the rails relative to the train. If this displacement exceeds the working depth of field indicated by the dotted line in the diagram, speed measurement will fail. The working depth of field of the laser Doppler speed measuring device is shown below. The expression is: ; In the formula: δ The diameter of the output beam after the two probe beams pass through the first fiber collimator 3 or the second fiber collimator 4. α The measurement half-angle of the laser Doppler train speed measuring device.

[0036] In this invention, the two fiber optic collimators in the laser Doppler train speed measuring device are mounted on the adjustment auxiliary platform of the electric slide rail unit 9. By rotating the adjustment auxiliary platform, the emission angle of the two detection beams can be changed, thereby enabling the speed measuring device to measure the half-angle. α The adjustment. When the interval between the two adjustment auxiliary platforms in the laser Doppler train speed measuring device is fixed at a certain value... d By adjusting the emission angle of the two fiber optic collimators through two auxiliary adjustment platforms, the measuring half-angle of the velocity measuring device is changed from... α 1 changes to α 2. The working depth of field of the laser Doppler train speed measuring device is determined by... L d1 Change to L d2 Meanwhile, the working distance of the speed measuring device is increased from... L M1 Change to L M2 According to the above formula, when the included angle... α The larger the value, the greater the working distance of the laser Doppler train speed measuring device. L M The shorter the working depth of field, the greater its depth of field. L d The shorter the angle, the better. Therefore, the measuring half-angle of the speed measuring system can be changed through the aforementioned adjustment auxiliary platform. α This allows for adjustment of the working depth of field, effectively suppressing the impact of train vibration on the measurement results and significantly improving the measurement robustness of the speed measuring device.

[0037] refer to Figure 4 The figure shows a schematic diagram of the working distance adjustment of a laser Doppler train speed measuring device that supports independent step-by-step adjustment of working depth of field and working distance, according to an embodiment of the present invention. Working distance L M Defined as the perpendicular distance from the maximum position of the convergence region of the two probe beams (i.e., the point of highest energy concentration) to the line connecting the two fiber collimators, its expression is as follows: ; In the formula: d The horizontal distance between the two fiber collimators is [missing information]. α This refers to the half-angle of the laser Doppler train speed measuring device. The working depth of field of the laser Doppler speed measuring device is adjusted by adjusting the auxiliary platform. L d Once adjusted to the appropriate position, the included angle can be locked. α .

[0038] This invention includes the aforementioned electric slide rail unit, and both fiber optic collimators are mounted on the adjustment auxiliary platform of the electric slide rail unit. The working depth of field of the laser Doppler train speed measuring device... L d Adjustment complete (i.e., measuring half the included angle) α After fixing, adjust the distance between the two adjustment auxiliary platforms. d The working distance of the device can be flexibly adjusted. L M As shown in the figure, the distance between the two adjustment auxiliary platforms on the electric slide rail unit is adjusted by... d 1 changes to d 2. The working distance of the laser Doppler train speed measuring device is determined by... L M1 Change to L M2 According to the above formula, when the spacing d The larger the value, the greater the working distance of the laser Doppler train speed measuring device. L M The longer. Therefore, the distance between the two adjustment auxiliary platforms on the electric slide rail unit is adjusted. d This allows for changing the working distance of the speed measuring device, thus flexibly adapting to the speed measuring installation conditions of different types of rail transit trains (such as wheel-rail trains or maglev trains).

[0039] In this embodiment, the narrow-linewidth continuous laser has an output power of 100 mW and an operating wavelength of 1550 nm. After collimation using an F260APC-1550 fiber optic collimator, the probe beam's spot diameter δ is 3 mm. The frequency shift of the acousto-optic modulator is 80 MHz. The velocity measuring device measures the half-angle of the laser beam. αThe angle is set to 3°, its value determined by the train's vibration, to determine the device's working depth of field; the distance d between the two fiber collimators is 6 cm, determined by the actual working distance of the train. Therefore, the working depth of field of the laser Doppler train speed measuring device is 57.2 mm, and the working distance is 57.2 cm. When the train speed is 100 km / h, the corresponding laser Doppler frequency shift signal is 1.876 MHz; while the beat frequency signal acquired by the detector depends on the train's direction of travel: 81.876 MHz for forward movement and 78.124 MHz for reverse movement. It should be noted that the laser's output power and working wavelength can be selected as needed; the detection beam diameter is determined by the selected fiber collimator; the frequency shift of the acousto-optic modulator can be determined based on the speed measurement range and the half-angle of the measurement; the half-angle of the measurement... α The working depth of field is determined by the vibration conditions of the train operation; the distance between the two fiber optic collimators d It is determined by the actual working distance of the train.

[0040] The following experimental results were used to verify the effect of introducing a plano-concave cylindrical lens beam expander on the signal-to-noise ratio (SNR) of the laser Doppler velocimetry device. The experimental results show that after adding a plano-concave cylindrical lens to the velocimetry optical path to expand the probe beam, the SNR of the received signal decreases. In the comparative experiment, the laser source was a 1550 nm DFB laser manufactured by Shanghai Konet Co., Ltd., with an output optical power of 100 mW; the photodetector was a Keyang Optoelectronics APD detector (model: KY-APRM-150M-I-FS-500 μm); the velocimetry device's half-angle was set to 7°; the acousto-optic modulator was a 40 MHz frequency-shifting acousto-optic modulator manufactured by Wuhan Zhongke Ruizhe Optoelectronics Technology Co., Ltd.; the receiving end converging lens had a diameter of 1.5 inch and a focal length of 75 mm; the plano-concave cylindrical lens was a Thorlabs LK1419RM-C model with a focal length of [missing information]. 150mm. The experimental target was a stainless steel turntable with a diameter of 8mm, driven by a motor. The turntable's rotational speed was continuously varied by adjusting the motor's drive voltage, and a laser Doppler velocimetry device was used to measure the linear velocity at the turntable's edge. The two sets of comparative experiments were conducted under identical conditions regarding laser source parameters, detector parameters, optical path geometry, and the object being measured. The only difference was that one set of experiments used a plano-concave cylindrical lens after the fiber collimator to expand the aligned beam; the other set of experiments did not use this beam-expanding lens.

[0041] During the comparative experiment, speed measurement results and corresponding signal-to-noise ratio (SNR) data were obtained under different rotational speed conditions. The experimental results are shown in the table. The experimental data shows that within the same or similar speed measurement range, the overall SNR of the echo signal obtained by the laser Doppler velocimetry system without a beam expander is higher than that of the system with a plano-concave cylindrical lens beam expander. There is a correlation between the speed measurement SNR and the speed measurement error; a higher SNR helps improve speed measurement accuracy and reduce speed measurement error. Therefore, the laser Doppler train speed measuring device proposed in this invention can achieve independent adjustment of the working depth of field without the need for a plano-concave cylindrical lens beam expander, thereby effectively avoiding the SNR decrease problem caused by beam diffusion and further improving the measurement stability and accuracy of the speed measuring device in actual vibration environments. Compared with speed measuring devices that introduce a plano-concave cylindrical lens beam expander, this invention has more prominent technical advantages in terms of SNR performance and system robustness.

[0042]

[0043] Furthermore, the slide rail unit of this invention also possesses a feedback adjustment function. During the actual operation of the laser Doppler speed measuring device, when the train experiences significant vibration, causing the measured rail to deviate from the effective working depth of field of the speed measuring device, the speed measurement signal cannot be properly calculated because an effective beat frequency signal cannot be formed. When the speed measuring device detects a speed calculation failure or speed measurement anomaly, the laser Doppler train speed measuring device feeds back the corresponding failure information to the host computer software. The host computer software generates control commands based on this feedback information and sends them to the processor; the processor drives the slide rail unit to move through a closed-loop control method, adjusting the distance between the two adjustment auxiliary platforms, thereby achieving real-time adjustment of the working distance, allowing the rail to re-enter the effective working depth of field and restoring the speed measuring function. Through the above-mentioned feedback closed-loop adjustment mechanism, the adaptive capability, stability, and reliability of the speed measuring device under strong vibration conditions can be significantly improved.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A laser Doppler train speed measuring device that supports independent step-by-step adjustment of working depth of field and working distance, characterized in that, include: The light source module is used to emit a first probe light and a second probe light with a set wavelength; An optical module is used to receive the first and second detection beams. Through train speed measurement, it receives beat frequency signals containing Doppler frequency shift information scattered back from the rail surface by the first and second detection beams. The optical module includes a slide rail unit, a first fiber optic collimator for receiving the first detection beam, and a second fiber optic collimator for receiving the second detection beam. The first and second fiber optic collimators are symmetrically arranged on both sides of the midpoint of the slide rail unit and can move synchronously towards or away from each other. The optical module supports step-by-step independent adjustment modes: Mode I: Adjusting the angle between the first and second detection beams on the rail surface by adjusting the angle of the first and second fiber optic collimators to adjust the working depth of field; Mode II: Adjusting the distance between the first and second fiber optic collimators using the slide rail unit to adjust the working distance. The processor is used to receive the beat frequency signal and calculate the train speed measurement information.

2. The laser Doppler train speed measuring device supporting independent step-by-step adjustment of working depth of field and working distance as described in claim 1, characterized in that, The working depth of field is defined as the difference between the maximum and minimum working distances at which the laser Doppler train speed measuring device can achieve effective speed measurement.

3. The laser Doppler train speed measuring device supporting independent step-by-step adjustment of working depth of field and working distance as described in claim 1, characterized in that, The light source module includes a narrow linewidth continuous laser and a 1-to-2 fiber beam splitter. The narrow linewidth continuous laser is used to emit a narrow linewidth probe laser beam with a set wavelength, and the 1-to-2 fiber beam splitter is used to split the narrow linewidth probe laser beam into a first probe beam and a second probe beam.

4. The laser Doppler train speed measuring device supporting independent step-by-step adjustment of working depth of field and working distance as described in claim 1, characterized in that, The optical module further includes a first adjustment auxiliary platform and a second adjustment auxiliary platform. The first adjustment auxiliary platform and the second adjustment auxiliary platform are symmetrically arranged on both sides of the midpoint of the slide rail unit and can perform synchronous movements in opposite directions or back directions. The first fiber collimator is fixed on the first adjustment auxiliary platform and the second fiber collimator is fixed on the second adjustment auxiliary platform.

5. The laser Doppler train speed measuring device supporting independent step-by-step adjustment of working depth of field and working distance according to claim 4, characterized in that, The first adjustment auxiliary platform and the second adjustment auxiliary platform are respectively provided with angle scale markings to assist in reading the convergence angle of the first detection light and the second detection light on the rail surface.

6. The laser Doppler train speed measuring device supporting independent step-by-step adjustment of working depth of field and working distance according to claim 4, characterized in that, The slide rail unit is equipped with distance scale markings to assist in adjusting the distance between the first adjustment auxiliary platform and the second adjustment auxiliary platform.

7. The laser Doppler train speed measuring device supporting independent step-by-step adjustment of working depth of field and working distance according to claim 1, characterized in that, The optical module also includes an acousto-optic modulator and an acousto-optic modulator driver. The acousto-optic modulator is used to introduce a set initial frequency to the beat frequency signal generated by the convergence of the first and second probe lights on the rail surface. The acousto-optic modulator driver is used to provide a high-frequency electrical signal to the acousto-optic modulator.

8. The laser Doppler train speed measuring device supporting independent step-by-step adjustment of working depth of field and working distance according to claim 1, characterized in that, The optical module also includes a converging lens and a photodetector. The converging lens is located at the midpoint of the slide rail unit. The converging lens is used to receive the backscattered light when the first and second probe lights are scattered on the rail surface, and couples the backscattered light into the photodetector for photoelectric conversion to obtain a beat frequency signal.

9. The laser Doppler train speed measuring device supporting independent step-by-step adjustment of working depth of field and working distance according to claim 1, characterized in that, It also includes a power supply module for supplying power to the light source module, the optical module and the processor.

10. A laser Doppler train speed measurement method, characterized in that, include: The laser Doppler train speed measuring device, which supports independent step-by-step adjustment of working depth of field and working distance as described in any one of claims 1-9, is installed on the bottom of the train to be measured, and the first detection light and the second detection light are made to illuminate the surface of the rail. The train under test is operated, and the train speed is measured using the laser Doppler train speed measuring device to obtain the train speed information of the train under test, wherein the train speed information includes speed, direction and distance.

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