Distance measuring instrument for geological survey and distance measuring method thereof

Abstract

The invention relates to the technical field of distance measurement, and discloses a distance measuring instrument for geological survey and a distance measuring method of the distance measuring instrument for geological survey. A first included angle is formed between the optical axis of the main receiving lens and the laser emergent optical axis of the semiconductor laser; and the main photoelectric detector is arranged near the focal plane of the receiving lens and is used for outputting a first electric signal. Through the original monitoring mode design, low-power-consumption operation of the auxiliary detector and the laser is only kept when no target exists, in the mode, low-power-consumption operation of the auxiliary channel and the microprocessor core is only needed, the main channel photoelectric detector with the highest power consumption and the processing circuit of the main channel photoelectric detector are completely powered off, and the effect of nearly zero idle power consumption is achieved.

Description

Technical Field

[0001] This invention relates to the field of distance measurement technology, specifically to a distance measuring instrument for geological surveying and its distance measurement method. Background Technology

[0002] Geological surveys, topographic mapping, and other field operations often require rapid and accurate non-contact measurements of the distances and shapes of rock masses, surfaces, and man-made structures. To meet this need, a rangefinder specifically designed for this field has been developed. Its core function is to stably and efficiently acquire high-precision distance data in complex terrain and variable environmental conditions.

[0003] Currently, portable ranging devices on the market generally employ laser triangulation as their core ranging principle to achieve high accuracy. A typical device typically consists of the following modules: a laser emitting module (usually a semiconductor laser and its driving circuit), an optical receiving module (composed of a receiving lens and a narrowband filter, used to collect reflected light and suppress stray light), a photoelectric detection module (such as a position-sensitive detector (PSD) or a CMOS image sensor, used to convert optical signals into electrical signals), and a signal processing and control module (usually based on a microcontroller (MCU), responsible for calculating distance and controlling the device's operation). Its basic workflow is as follows: the laser emits a beam of light to the target object; some of the reflected light is focused by the receiving lens, forming a light spot on the photosensitive surface of the detector; by precisely calculating the offset of the light spot's imaging position, and combining this with the fixed baseline distance formed between the laser emitting axis and the receiving axis, the precise distance to the target object can be calculated based on trigonometric geometry principles.

[0004] However, traditional triangulation laser rangefinders have revealed a series of technical bottlenecks when adapted to the complex field environments of modern geological surveys. Among them, the problem of insufficient battery life caused by high power consumption is particularly prominent. At the same time, other limiting factors seriously affect the practicality of the equipment.

[0005] In pursuit of immediate response, existing equipment operates at full power continuously once powered on, resulting in persistently high power consumption. While strategies such as manual power-on / off or automatic sleep mode at fixed intervals are commonly used for power management, these methods are extremely inefficient in actual field operations. Frequent manual operations disrupt the survey process, and relying on user-remembered power-off operations is highly unreliable, ultimately failing to meet the stringent requirements for endurance during long-term continuous operation. Therefore, this invention provides a rangefinder for geological surveying and its ranging method. Summary of the Invention

[0006] To address the aforementioned shortcomings of existing technologies, this invention provides a rangefinder for geological surveying and its ranging method.

[0007] This invention provides the following technical solution: a rangefinder for geological surveying, comprising a semiconductor laser, a converging lens disposed on the laser emission path of the laser, a main receiving lens whose optical axis forms a first angle with the laser emission optical axis of the semiconductor laser, and a main photodetector disposed near the focal plane of the receiving lens for outputting a first electrical signal; further comprising:

[0008] The secondary receiving lens is located on the side of the converging lens and below the main receiving lens. It is used to receive specific optical signals from the laser transmission path, and its optical axis forms a second angle with the laser output optical axis.

[0009] The secondary photodetector is located on the image side of the secondary receiving lens and is used to receive the laser signal reflected by the target and output a second electrical signal.

[0010] The signal processing and control unit is electrically connected to the semiconductor laser, the main photodetector, and the secondary photodetector, respectively. During measurement, it controls the semiconductor laser to switch between monitoring mode and measurement mode.

[0011] In monitoring mode, the semiconductor laser is controlled to periodically emit low duty cycle detection pulses, while the main photodetector is in a completely dormant state and identifies the target.

[0012] The measurement mode operates by continuously emitting laser or high duty cycle pulses and activating the main photodetector.

[0013] The system synchronously acquires the first electrical signal output by the main photodetector and the second electrical signal output by the secondary photodetector; it calculates the initial sub-pixel accuracy position value N0 of the light spot on the main photodetector based on the first electrical signal, and obtains the intensity value S of the second electrical signal. aux Based on the initial position value N0 and the intensity value S aux The distance lookup table stored in the memory is consulted to obtain the initial reference value Z0 of the absolute distance from the rangefinder to the measured surface; the final high-precision distance value Z is then calculated based on the first electrical signal.

[0014] Finally, material identification is performed based on the second electrical signal, and the initial reference value Z0 is compensated and corrected using the corresponding reflectivity compensation coefficient. The final distance value Z after material adaptive correction is then output. final .

[0015] Preferably, the switching operation of the semiconductor laser between monitoring mode and measurement mode is as follows:

[0016] During measurement, the semiconductor laser is controlled to periodically emit low duty cycle probe pulses to enter the listening mode. During the intervals between the emitted probe pulses, the main photodetector is put into a low-power sleep state.

[0017] Within the time window of transmitting the detection pulse, the second electrical signal output by the auxiliary photodetector is collected. When the intensity value of the second electrical signal exceeds the preset threshold in multiple consecutive pulse cycles, it is determined to be a valid target and a digital trigger signal is generated.

[0018] In response to a digital trigger signal, the semiconductor laser is controlled to switch to the measurement mode and operates by continuously emitting laser or high duty cycle pulses. At the same time, the main photodetector is activated to normal operating status, achieving extremely low power consumption through mode switching.

[0019] Preferably, the strength threshold operation of the second electrical signal of the signal processing and control unit is as follows:

[0020] The intensity value of the second electrical signal is statistically analyzed in real time, and its moving average value μ and standard deviation σ are calculated. The preset threshold is dynamically adjusted to T=μ+K·σ, where K is an adjustable coefficient. A digital trigger signal is generated only when the intensity value of the second electrical signal exceeds the dynamically adjusted threshold T in multiple consecutive pulse cycles.

[0021] Preferably, the initial distance measurement value in the signal processing and control unit is calculated as follows:

[0022] The initial sub-pixel position value N0 of the light spot on the main photodetector is calculated based on the first electrical signal, and the intensity value S of the second electrical signal output by the secondary photodetector is collected. aux Based on the initial position value N0 and the intensity value S aux The system queries the distance lookup table pre-stored in the signal processing and control unit memory. The distance lookup table stores the secondary electrical signal strength value S. aux The mapping relationship between the main spot position value N0 and the absolute distance value Z0 is used to obtain the absolute distance value from the rangefinder to the measured surface, which is the initial reference value Z0.

[0023] Preferably, the signal processing and control unit operates as follows when querying the distance lookup table:

[0024] The initial position value N0 of the light spot calculated based on the first electrical signal and the intensity value S of the second electrical signal. aux When a query is performed, the distance lookup table will return multiple possible candidate values ​​for absolute distance;

[0025] The auxiliary photodetector acts as a one-dimensional PSD position-sensitive detector, reading the analog voltage signal X output by the one-dimensional PSD, which is proportional to the one-dimensional centroid position of the light spot. i According to the formula Dcoarse=(B×F) / (X) i +X0) calculates a rough distance prior value Dcoarse;

[0026] Where B is the baseline distance between the optical center of the secondary receiving lens and the center of the output aperture of the semiconductor laser, F is the focal length of the secondary receiving lens, and X0 is the system zero-position calibration offset.

[0027] The coarse distance prior value Dcoarse is compared with multiple absolute distance candidate values, and the value closest to Dcoarse is selected as the effective initial absolute distance reference value Z0.

[0028] Preferably, the final distance value Z is calculated as follows:

[0029] After obtaining the initial absolute distance reference value Z0, the first electrical signal is continuously acquired and the real-time position value N_(current) of the light spot is calculated. The offset ΔN of the light spot is calculated according to the formula ΔN=N_(current)-N0.

[0030] The relative displacement change ΔM relative to the initial absolute distance Z0 is calculated using the formula ΔM=f(ΔN,L',α), where L' is the image distance and α is the angle between the optical axis of the main receiving lens and the optical axis of the laser emission lens.

[0031] The high-precision absolute distance value Z is synthesized and output using the formula Z=Z0+ΔM×C, where C is the conversion coefficient determined by the geometric parameters of the optical system.

[0032] Preferably, the final distance measurement process in the signal processing and control unit is as follows:

[0033] The time-domain waveform of the second electrical signal output by the auxiliary photodetector is acquired, and the characteristic parameters of the time-domain waveform are extracted. The characteristic parameters include one or more of the following: pulse width, rise time, and fall time.

[0034] The extracted feature parameters are matched with the material feature library pre-stored in the memory to output the type identification result of the surface material of the target being tested;

[0035] Based on the material type identification result, obtain the corresponding reflectivity compensation coefficient. Use the reflectivity compensation coefficient to compensate and correct the calculated distance measurement value, and obtain the proportional compensation coefficient 'a' corresponding to the material. M and offset compensation coefficient b M Using formula Z final =(1-a M )×Zb M The final distance value Z after compensation is calculated. final It also outputs the measurement results.

[0036] A distance measurement method for geological surveying, the specific operation of which is as follows:

[0037] S1. Control the semiconductor laser to periodically emit low duty cycle probe pulses to enter the listening mode, and put the main photodetector into a sleep state during the pulse interval.

[0038] S2. Acquire the second electrical signal output by the secondary photodetector within the time window of the emission pulse. When the intensity of the second electrical signal exceeds the dynamic threshold for multiple consecutive cycles, generate a trigger signal and switch to the measurement mode.

[0039] S3. Control the semiconductor laser to operate in continuous emission or high duty cycle pulse mode, and activate the main photodetector.

[0040] S4. Synchronously acquire the first electrical signal and the second electrical signal, calculate the sub-pixel accuracy position value N0 of the light spot based on the first electrical signal, and combine it with the intensity value S of the second electrical signal. aux Query the distance lookup table to obtain the initial absolute distance baseline value Z0;

[0041] S5. Calculate the real-time position offset of the light spot based on the first electrical signal, and combine the optical system parameters to calculate the relative displacement change, synthesizing a high-precision absolute distance value Z. Analyze the time-domain characteristics of the second electrical signal for material identification, obtain the corresponding reflectivity compensation coefficient, and use the compensation coefficient to correct the distance value Z, outputting the final distance value Z. final .

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] (1) Through the original listening mode design, only the secondary detector and laser are kept running at low power when there is no target. In this mode, only the secondary channel and microprocessor core need to keep running at low power, while the main channel photodetector and its processing circuit, which have the highest power consumption, are completely powered off, achieving an effect of almost "zero idle power consumption". This is crucial for field geological survey equipment that relies on battery power, enabling it to extend its working time from several hours to several days or even several weeks.

[0044] (2) The intelligent triggering algorithm based on sliding window weighted statistics and dynamic threshold can effectively distinguish between ambient stray light and valid target echo, greatly reducing the false triggering rate and ensuring that the device only enters the high power measurement mode when a real target is detected, thus achieving a perfect balance between power consumption and performance.

[0045] (3) By combining high-precision main channel LUT query with fast secondary channel PSD coarse distance measurement, when the LUT returns multiple candidate values, the prior distance information provided by the secondary channel is used for arbitration, and the only correct initial absolute distance value is intelligently selected. This fundamentally avoids result jumps and errors in medium and long distance measurements and greatly extends the reliable measurement range.

[0046] (4) First, the absolute distance reference is calculated, and then the nanometer-level / micrometer-level change relative to the absolute distance reference is calculated by monitoring the tiny displacement of the light spot at the sub-pixel level on the PSD / CMOS. Finally, a high-precision result is synthesized. This method improves the measurement accuracy to a level far exceeding that of the traditional single triangulation method.

[0047] (5) By utilizing the time-domain and even frequency-domain characteristics of the echo signal of the secondary channel, the target material type is determined by the pattern recognition algorithm, and the pre-calibrated material compensation coefficient library is called to perform real-time linear compensation of the measurement results. This significantly reduces the measurement error caused by the change of the material of the target being measured, and improves the practicality of the rangefinder from the standard whiteboard in the laboratory to complex field geological environments. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of the laser path structure during measurement in this invention;

[0049] Figure 2 This is a schematic diagram of the component structure of the present invention;

[0050] Figure 3 This is a flowchart illustrating the monitoring mode and triggering process of the present invention;

[0051] Figure 4 This is a flowchart of the high-precision measurement and material compensation process of the present invention. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. In order to keep the following description of the embodiments of this disclosure clear and concise, detailed descriptions of known functions and known components are omitted to avoid unnecessarily obscuring the concept of the present invention.

[0053] Please see Figure 1 and Figure 2 A geological survey rangefinder, comprising the following components:

[0054] Semiconductor laser: Select a pulsed laser diode with high peak power and small divergence angle, with a wavelength of, for example, 905nm. It needs to have a driving circuit, be able to accept external TTL signals, and quickly switch between narrow pulses of less than 100ns (listening mode) and continuous wave / high duty cycle pulses (measurement mode).

[0055] Converging lens: Installed on the laser reflection path of the laser, the aspherical design collimates and converges the laser beam, effectively reducing the beam divergence angle and ensuring that a clear and concentrated measurement spot is formed when the laser is transmitted to a distant target surface, laying the foundation for the subsequent receiving module to obtain a stable echo signal.

[0056] Main receiving lens: A large-aperture, long-focal-length lens is used to collect more reflected light and improve the signal-to-noise ratio. The first angle α between its optical axis and the laser emission optical axis is set to 15°-30° to form a triangulation baseline.

[0057] Secondary receiving lens: Located below and to the side of the converging lens, a lens with a relatively small aperture is selected. The second angle β between its optical axis and the laser axis should be greater than the first angle α to ensure sufficient signal strength even at close range.

[0058] Main photodetector: Employs a one-dimensional or two-dimensional position-sensitive detector (PSD) or a high-speed area array CMOS / CCD sensor. PSDs offer advantages such as fast response speed, high position resolution (achieving sub-pixel accuracy), and lower cost; CMOS sensors provide complete image information and have stronger anti-interference capabilities. It is precisely positioned near the focal plane of the main receiving lens.

[0059] Secondary photodetector: This device has dual functions.

[0060] Target recognition function: As a simple photodiode, it is used to quickly detect the presence or absence of light pulses.

[0061] Coarse ranging / material recognition function: As a one-dimensional PSD, it is used to output an analog voltage signal X related to the centroid position of the light spot. i .

[0062] Therefore, the preferred solution is to directly select a one-dimensional PSD as the secondary detector.

[0063] In addition, in order to suppress ambient stray light interference to the greatest extent, it is recommended to install a narrowband interference filter with a center wavelength matching the laser wavelength in front of each of the main and secondary receiving lenses. This filter is not shown in the figure.

[0064] Signal processing and control unit:

[0065] Core processor: This is the control and computing center of the device, responsible for coordinating the work of various modules, processing acquired data, and outputting the final results. It mainly includes a signal processing unit and connecting circuits. The core of the signal processing unit is a high-performance processor. A high-performance ARM Cortex-M4 / M7 core microcontroller (MCU) should be selected, with a recommended clock frequency of over 200MHz. It should also have a built-in floating-point unit (FPU) to meet the needs of real-time signal processing.

[0066] Simultaneously equipped with analog front-end circuitry, the secondary channel must include a high-speed, high-gain transimpedance amplifier (TIA) to convert the photocurrent signal output from the secondary PSD into a voltage signal.

[0067] Sub-channel: It needs to include a high-speed, high-gain transimpedance amplifier (TIA) to convert the photocurrent signal of the sub-PSD into a voltage signal.

[0068] Main channel: If PSD is used, the corresponding current-to-voltage conversion and addition / subtraction circuits are required to calculate the spot position.

[0069] Analog-to-digital converter (ADC): At least two high-speed ADC channels (>=10MSPS) are required to synchronously acquire signals from the main and secondary channels.

[0070] Memory: The MCU needs to be expanded with an external SPI Flash memory to store the large distance lookup table (LUT) and material feature library and compensation coefficient library.

[0071] Laser drive circuit: Controlled by the MCU's I / O port through MOSFET or a dedicated laser drive chip to achieve rapid switching of emission modes.

[0072] A distance measurement method for geological surveying, the specific operation procedure is as follows:

[0073] The process for switching between monitoring mode and measurement mode is as follows: (See attached document) Figure 3 ;

[0074] Upon power-up, the device defaults to a low-power monitoring mode. During this mode, the power supply to the main photodetector and its front-end circuitry is completely cut off, placing them in a sleep state. Only the secondary photodetector and the semiconductor laser remain operational to minimize power consumption. The MCU in the signal processing unit controls the laser driver, driving the semiconductor laser to periodically emit short pulses at a low frequency and low duty cycle, for example, a frequency of 1kHz and a pulse width of 100ns. After each laser pulse emission, the MCU synchronously acquires the signal output from the secondary channel via an ADC, extracting the light intensity value S. aux .

[0075] To avoid misjudgments caused by stray light from the environment, such as sunlight and reflected light from vegetation, the algorithm will continuously update the collected S... aux Statistical analysis is performed; a sliding window weighted statistical algorithm is used here, and the specific implementation logic is as follows:

[0076] Sliding window setting: Acquire S with a fixed number of pulse cycles (e.g., 100 pulse cycles). aux data);

[0077] Weighted strategy: Each data point within the window is assigned a different weight based on its age. Newer data has a higher weight, and older data has a lower weight. Specifically, the weight W of the i-th data point within the window (i ranges from 1 to 100, where 1 is the oldest and 100 is the newest) is... i The calculation formula is: W i =i / Σ i (where Σ)i The sum of integers from 1 to 100 (i.e., 5050) ensures the timeliness of data processing while also suppressing the interference of single outliers to a certain extent.

[0078] Dynamic threshold calculation: Based on this weighted window, the algorithm calculates two key statistics:

[0079] Weighted moving average μ is calculated using the formula: ,in The light intensity value collected during the i-th pulse cycle within the window. The weight corresponding to the i-th light intensity value is summed using the symbol Σ. i This indicates that the calculation is performed by accumulating all data points within the sliding window;

[0080] Standard deviation σ is calculated using the formula: Calculate the weighted standard deviation of the data within the window, reflecting S aux The degree of fluctuation;

[0081] Dynamic threshold T determination: Adjust the judgment threshold according to the formula "T=μ+K·σ", where K is an adjustable coefficient according to the environment, with a default value of 3-5. The value of K can be configured through the host computer of the device. In strong light environment, K is set to 5 to increase the threshold and avoid false triggering. In cloudy or low light environment, K is set to 3 to decrease the threshold and ensure that the trigger is not missed. For example, when μ=2.4V, σ=0.155V, and K=3, T=2.4+3×0.155≈2.865V.

[0082] The dynamic threshold enables the system to effectively distinguish between laser echo signals and environmental stray light noise (such as sunlight and vegetation reflection), greatly reducing the false alarm rate and ensuring that measurement is only activated when a real target is detected.

[0083] Using a fixed number of pulse periods (e.g., 100 pulses) as a sliding window, calculate S within the window. aux The moving average μ and standard deviation σ are used to dynamically adjust the judgment threshold according to the formula "T=μ+K·σ", where K is an adjustable coefficient according to the environment, with a default value of 3-5.

[0084] When S occurs within N consecutive pulse cycles (e.g., 5 cycles) aux When all values ​​exceed the dynamic threshold T, the system determines that a valid target has been detected, immediately generates a trigger signal, wakes up the dormant main photodetector and its front-end circuit, and controls the laser to switch to measurement mode; if the trigger condition is not met, the monitoring mode continues to cycle.

[0085] After the trigger signal is generated, the device immediately enters the high-precision measurement mode: the MCU controls the laser to switch to continuous emission or high duty cycle pulse mode (such as duty cycle 50%) to ensure that the target surface is sufficiently irradiated by laser. At the same time, the main photodetector and its front-end circuit are powered on to activate their normal operation, and then the main and auxiliary channel signals are acquired synchronously and at high speed.

[0086] Precise measurement process: See Figure 4 ;

[0087] In the distance calculation stage, an initial absolute distance is first calculated to address the inherent multi-value problem in triangulation. The initial position value N0 of the light spot with sub-pixel precision calculated by the main channel is then compared with the light intensity value S extracted by the secondary channel. aux The distance lookup table (LUT) pre-stored in the SPI Flash memory is consulted as the key. If the LUT returns a unique distance value, it is directly used as the initial absolute distance reference value Z0.

[0088] If the LUT returns multiple candidate distance values ​​(which is a common case), then the analog voltage signal X, which is related to the centroid position of the light spot, is output from the secondary PSD. i According to the formula Dcoarse=(B×F) / (X) i +X0), calculate the coarse distance prior value, where B is the baseline distance between the semiconductor laser and the optical center of the secondary receiving lens, F is the focal length of the secondary receiving lens, and X0 is the system null calibration value. Then compare the coarse distance prior value with multiple candidate values ​​returned by the LUT, and select the closest candidate value as the final absolute distance initial reference value Z0.

[0089] Based on the initial reference value, the high-precision distance is further calculated: the real-time position value N_(current) of the continuously output light spot of the main photodetector is used to calculate the offset ΔN of the light spot relative to the initial position according to the formula ΔN=N_(current)-N0; combined with optical parameters such as the image distance L' of the main receiving lens and the angle α between the optical axis of the main receiving lens and the laser emission optical axis, the small displacement change ΔM relative to Z0 is calculated through the geometric relationship formula "ΔM=f(ΔN,L',α)"; finally, the high-precision absolute distance value Z is synthesized according to the formula "Z=Z0+ΔM×C", where C is the conversion coefficient determined by the optical structure of the system.

[0090] Material compensation process:

[0091] The surface materials and reflectivity of different geological targets (such as granite, limestone, soil, and concrete) vary, which leads to different characteristics of laser echo signals and thus affects the ranging accuracy. Therefore, material adaptive compensation is needed to eliminate this error.

[0092] First, material identification is performed: The MCU analyzes the time-domain waveform of the secondary channel signal acquired in measurement mode and extracts the waveform's characteristic parameters, including pulse width (FWHM), rise time (time to rise from 10% amplitude to 90% amplitude), and fall time (time to fall from 90% amplitude to 10% amplitude). The extracted characteristic parameters are matched with the material feature library pre-stored in the SPI Flash memory. The nearest neighbor algorithm or a small-scale neural network can be used to identify the most likely material type of the target being measured. This is an existing technology. In addition, frequency domain features are added as an auxiliary criterion. By performing FFT (Fast Fourier Transform) analysis on the echo signal and extracting its spectral features, the reflection characteristics of different materials can be better distinguished.

[0093] Error compensation is then performed: based on the identified material type, the pre-calibrated scaling factor 'a' is read from the compensation factor library in memory. M and offset compensation coefficient b M Using formula Z final =(1-a M )×Zb M The high-precision distance value Z is then compensated to obtain the final distance value Z that eliminates the influence of material reflection differences. final Finally, Z final The distance measurement process can be completed by visually displaying the data on the device's screen or transmitting it to an external survey terminal via a data interface (such as USB or RS485).

[0094] To ensure the ranging accuracy of the equipment, the distance lookup table (LUT), material compensation library, and system zero point pre-calibration must be completed before leaving the factory. The specific process is as follows:

[0095] (a) Distance Lookup Table (LUT) calibration

[0096] A standard white diffuse reflective target plate with known and stable reflectivity is fixed on a high-precision guide rail. The target plate is slowly moved from the nearest to the farthest measurement distance of the equipment in fixed steps (e.g., 1 cm). At each moving position, the known true distance Z of that position is recorded. truth Simultaneously, the initial position value N0 of the light spot in the main channel and the light intensity value S in the secondary channel of the acquisition device are collected. aux , forming "Z truth -N0-S aux The mapping relationship data of "" is processed; after organizing the mapping relationship data collected from all locations, it is stored in the device's SPIFlash memory to generate a distance lookup table (LUT).

[0097] (II) Calibration of Material Compensation Library

[0098] Fix the standard target plate at a known absolute distance Z. truthPosition the target board to ensure its relative position to the equipment is stable; sequentially replace the standard target board with different materials (such as black lacquered board, cement board, granite board, soil sample board, etc.), ensuring that each material's target board maintains the same distance from the equipment; for each material's target board, measure the uncompensated original distance value Z output by the equipment. raw ; Calculate the ranging error (Error=Z) for each material. raw -Z truth ; Change the distance between the target board and the equipment, repeat the above measurement process, and obtain multiple sets of data for each material; for the multiple sets of data for each material, use the least squares method to fit the linear error equation "Error_M=a M ×Z raw +b M ", where a M b is the proportionality coefficient. M This is the offset coefficient; it sets the "material type a" corresponding to each material. M and b M "Data is stored in a memory to establish a material compensation library."

[0099] (III) System Zero-Point X0 Calibration

[0100] Select a calibration location with a known precise distance, and place a standard white diffuse reflective target plate at that location; start the equipment and enter measurement mode, and acquire the analog voltage signal X output by the secondary photodetector (one-dimensional PSD). i According to the formula for calculating the coarse distance of the secondary channel, "Dcoarse=(B×F) / (X)",... i "+X0")" and substitute the known baseline distance B, the focal length of the secondary receiving lens F, and the actual distance Z of the calibration position. truth (i.e., Dcoarse=Z) truth The system zero-point calibration value X0 is calculated in reverse; X0 is stored in the device's MCU internal register for calibration during subsequent coarse distance calculations.

[0101] The above embodiments are merely exemplary embodiments of the present invention and are not intended to limit the present invention. The scope of protection of the present invention is defined by the claims. Those skilled in the art can make various modifications or equivalent substitutions to the present invention within its spirit and scope of protection, and such modifications or equivalent substitutions should also be considered to fall within the scope of protection of the present invention.

Claims

1. A rangefinder for geological surveying, comprising a semiconductor laser, a converging lens disposed on the laser emission path of the laser, a main receiving lens whose optical axis forms a first angle with the laser emission optical axis of the semiconductor laser, and a main photodetector disposed near the focal plane of the receiving lens for outputting a first electrical signal; characterized in that, Also includes: The secondary receiving lens is located on the side of the converging lens and below the main receiving lens. It is used to receive specific optical signals from the laser transmission path, and its optical axis forms a second angle with the laser output optical axis. The secondary photodetector is located on the image side of the secondary receiving lens and is used to receive the laser signal reflected by the target and output a second electrical signal. The signal processing and control unit is electrically connected to the semiconductor laser, the main photodetector, and the secondary photodetector, respectively. During measurement, it controls the semiconductor laser to switch between monitoring mode and measurement mode. In monitoring mode, the semiconductor laser is controlled to periodically emit low duty cycle detection pulses, while the main photodetector is in a completely dormant state and identifies the target. The measurement mode operates by continuously emitting laser or high duty cycle pulses and activating the main photodetector. The system synchronously acquires the first electrical signal output by the main photodetector and the second electrical signal output by the secondary photodetector; it calculates the initial sub-pixel accuracy position value N0 of the light spot on the main photodetector based on the first electrical signal, and obtains the intensity value S of the second electrical signal. aux Based on the initial position value N0 and the intensity value S aux The distance lookup table stored in the memory is consulted to obtain the initial reference value Z0 of the absolute distance from the rangefinder to the measured surface; the final high-precision distance value Z is then calculated based on the first electrical signal. Finally, material identification is performed based on the second electrical signal, and the initial reference value Z0 is compensated and corrected using the corresponding reflectivity compensation coefficient. The final distance value Z after material adaptive correction is then output. final .

2. The rangefinder for geological surveying according to claim 1, characterized in that, The switching operation of the semiconductor laser between monitoring mode and measurement mode is as follows: During measurement, the semiconductor laser is controlled to periodically emit low duty cycle probe pulses to enter the listening mode. During the intervals between the emitted probe pulses, the main photodetector is put into a low-power sleep state. Within the time window of transmitting the detection pulse, the second electrical signal output by the auxiliary photodetector is collected. When the intensity value of the second electrical signal exceeds the preset threshold in multiple consecutive pulse cycles, it is determined to be a valid target and a digital trigger signal is generated. In response to a digital trigger signal, the semiconductor laser is controlled to switch to the measurement mode and operates by continuously emitting laser or high duty cycle pulses. At the same time, the main photodetector is activated to normal operating status, achieving extremely low power consumption through mode switching.

3. A distance measuring instrument for geological surveying according to claim 2, characterized in that, The intensity threshold operation of the second electrical signal of the signal processing and control unit is as follows: The intensity value of the second electrical signal is statistically analyzed in real time, and its moving average value μ and standard deviation σ are calculated. The preset threshold is dynamically adjusted to T=μ+K·σ, where K is an adjustable coefficient. A digital trigger signal is generated only when the intensity value of the second electrical signal exceeds the dynamically adjusted threshold T in multiple consecutive pulse cycles.

4. A rangefinder for geological surveying according to claim 1, characterized in that, The initial distance measurement value in the signal processing and control unit is calculated as follows: The initial sub-pixel position value N0 of the light spot on the main photodetector is calculated based on the first electrical signal, and the intensity value S of the second electrical signal output by the secondary photodetector is collected. aux Based on the initial position value N0 and the intensity value S aux The system queries the distance lookup table pre-stored in the signal processing and control unit memory. The distance lookup table stores the secondary electrical signal strength value S. aux The mapping relationship between the main spot position value N0 and the absolute distance value Z0 is used to obtain the absolute distance value from the rangefinder to the measured surface, which is the initial reference value Z0.

5. A rangefinder for geological surveying according to claim 4, characterized in that, The signal processing and control unit operates as follows when querying the distance lookup table: The initial position value N0 of the light spot calculated based on the first electrical signal and the intensity value S of the second electrical signal. aux When a query is performed, the distance lookup table will return multiple possible candidate values ​​for absolute distance; The auxiliary photodetector acts as a one-dimensional PSD position-sensitive detector, reading the analog voltage signal X output by the one-dimensional PSD, which is proportional to the one-dimensional centroid position of the light spot. i According to the formula Dcoarse=(B×F) / (X) i +X0) calculates a rough distance prior value Dcoarse; Where B is the baseline distance between the optical center of the secondary receiving lens and the center of the output aperture of the semiconductor laser, F is the focal length of the secondary receiving lens, and X0 is the system zero-position calibration offset. The coarse distance prior value Dcoarse is compared with multiple absolute distance candidate values, and the value closest to Dcoarse is selected as the effective initial absolute distance reference value Z0.

6. A rangefinder for geological surveying according to claim 1, characterized in that, The final distance value Z is calculated as follows: After obtaining the initial absolute distance reference value Z0, the first electrical signal is continuously acquired and the real-time position value N_(current) of the light spot is calculated. The offset ΔN of the light spot is calculated according to the formula ΔN=N_(current)-N0. The relative displacement change ΔM relative to the initial absolute distance Z0 is calculated using the formula ΔM=f(ΔN,L',α), where L' is the image distance and α is the angle between the optical axis of the main receiving lens and the optical axis of the laser emission lens. The high-precision absolute distance value Z is synthesized and output using the formula Z=Z0+ΔM×C, where C is the conversion coefficient determined by the geometric parameters of the optical system.

7. A rangefinder for geological surveying according to claim 1, characterized in that, The final distance measurement process in the signal processing and control unit is as follows: The time-domain waveform of the second electrical signal output by the auxiliary photodetector is acquired, and the characteristic parameters of the time-domain waveform are extracted. The characteristic parameters include one or more of the following: pulse width, rise time, and fall time. The extracted feature parameters are matched with the material feature library pre-stored in the memory to output the type identification result of the surface material of the target being tested; Based on the material type identification result, obtain the corresponding reflectivity compensation coefficient. Use the reflectivity compensation coefficient to compensate and correct the calculated distance measurement value, and obtain the proportional compensation coefficient 'a' corresponding to the material. M and offset compensation coefficient b M Using formula Z final =(1-a M )×Zb M The final distance value Z after compensation is calculated. final It also outputs the measurement results.

8. A distance measurement method for geological surveying, characterized in that, The specific operation of the geological survey rangefinder according to any one of claims 1-7 is as follows: S1. Control the semiconductor laser to periodically emit low duty cycle probe pulses to enter the listening mode, and put the main photodetector into a sleep state during the pulse interval. S2. Acquire the second electrical signal output by the secondary photodetector within the time window of the emission pulse. When the intensity of the second electrical signal exceeds the dynamic threshold for multiple consecutive cycles, generate a trigger signal and switch to the measurement mode. S3. Control the semiconductor laser to operate in continuous emission or high duty cycle pulse mode, and activate the main photodetector. S4. Synchronously acquire the first electrical signal and the second electrical signal, calculate the sub-pixel accuracy position value N0 of the light spot based on the first electrical signal, and combine it with the intensity value S of the second electrical signal. aux Query the distance lookup table to obtain the initial absolute distance reference value Z0; S5. Calculate the real-time position offset of the light spot based on the first electrical signal, and combine the optical system parameters to calculate the relative displacement change, synthesizing a high-precision absolute distance value Z. Analyze the time-domain characteristics of the second electrical signal for material identification, obtain the corresponding reflectivity compensation coefficient, and use the compensation coefficient to correct the distance value Z, outputting the final distance value Z. final .

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