Method for self-calibration of the delay of a telecommunication signal channel of a three-dimensional laser scanner

Abstract

The application provides a three-dimensional laser scanner electric signal channel delay self-calibration method, calculates the time difference between a transmitting pulse and a receiving pulse through the absolute distance between a target and the transmitting channel and the receiving channel, adds the fixed delay between a reference pulse and the transmitting pulse to the absolute time to obtain the absolute time as a reference; a data processing module sends an instruction to a transmitting module to control the transmitting module to send a pulse laser, and at the same time, the pulse laser sends a reference light beam to an analog amplification module as a reference signal; the pulse laser is irradiated on the target surface through a scanning mechanism, and the diffusely reflected light signal returns to the receiving channel, converges on a photosensitive element on the surface of an analog detection amplification module through the scanning mechanism, and the light signal is output to the data processing module as an electric signal of different channels through the analog detection amplification module; the data processing module compares the electric signal of different channels with the absolute time to calibrate the delay of the electric signal of different channels.

Description

Technical Field

[0001] This invention relates to the field of visibility meters, and in particular to a method for self-calibration of electrical signal channel delay in a three-dimensional laser scanner. Background Technology

[0002] The ranging range of a 3D laser scanner can cover distances from a few meters to hundreds or even thousands of meters, thanks to its multi-channel signal amplification, acquisition, and processing capabilities, enabling it to handle a wide dynamic range of signals. However, during data acquisition, the acquired echo light signal is converted into an electrical signal and then transmitted to the backend for data processing via multiple amplification circuits. This transmission inevitably introduces a certain delay between channels. Furthermore, changes in environmental factors such as temperature and humidity can alter the delay, thus affecting the ranging accuracy of the 3D laser scanner. Summary of the Invention

[0003] The main objective of this invention is to provide a self-calibration method for the delay of the electrical signal channel of a 3D laser scanner, which solves the problem that the delay of each channel may change with changes in environmental factors such as temperature and humidity, thereby affecting the ranging accuracy of the 3D laser scanner.

[0004] To solve the above technical problems, the technical solution adopted by the present invention is: a self-calibration method for delay of electrical signal channel of a three-dimensional laser scanner, S1, a fixed reflective target is installed at an angle position that the laser reflected by the internal scanning mirror of the three-dimensional laser scanner can sweep outside the working field of view, and the light rays at the target surface and the target center position are perpendicular.

[0005] S2. The optical path distance d1 between the target surface and the APD photosensitive surface is fixed, the distance d2 between the origin of the scanner coordinate system and the target surface is fixed, and the optical path distance d3 corresponding to the time difference between the emitted pulse and the received pulse should also be fixed.

[0006] Based on this feature, d1, d2, and d3 can be measured and acquired in real time as needed, either at the start of the scanner's operation or during the operation.

[0007] S3. Real-time calibration of the delay parameters of each channel ensures the consistency of the distance measurement benchmark for each channel, as well as the consistency of distance measurement between channels.

[0008] S4. Calculate the time difference between the transmitted pulse and the received pulse using the absolute distance between the target and the transmitting and receiving channels. Add this time difference to the fixed delay between the reference pulse and the transmitted pulse to obtain the absolute time as a reference.

[0009] S5. When the equipment is powered on, the data processing module sends a command to the scanning mechanism to stop the scanning mechanism from illuminating the target with the emitted laser.

[0010] The data processing module sends a command to the transmitting module to control the transmitting module to emit a pulsed laser. At the same time, the pulsed laser emits a reference beam to the analog amplification module as a reference signal.

[0011] The pulsed laser is irradiated onto the target surface by the scanning mechanism. The light signal reflected back by the diffuse reflection enters the receiving channel through the scanning mechanism and converges on the photosensitive element on the surface of the analog detection amplification module. The light signal is then output as electrical signals from different channels to the data processing module by the analog detection amplification module.

[0012] The data processing module compares the electrical signals of different channels with absolute time to calibrate the delay of the electrical signals of different channels.

[0013] In the preferred embodiment, after the device is powered on, the data processing module sends a command to the scanning mechanism to stop the scanning mechanism from illuminating the target with the emitted laser.

[0014] The data processing module sends a command to the transmitting module to control the transmitting module to emit pulsed laser. At the same time, the pulsed laser emits a reference beam to the analog amplification module as a reference signal. The data processing module controls the power of the emitted pulsed laser in real time, adjusting it from high to low.

[0015] The pulsed laser is irradiated onto the target surface by the scanning mechanism. The reflected light signal is then received by the scanning mechanism and converged on the photosensitive element on the surface of the analog detection amplification module. The light signal is then processed by the analog detection amplification module through photoelectric conversion and output as electrical signals from different channels to the data processing module.

[0016] The data processing module performs waveform analysis on the amplitude values ​​and reception time of electrical signals from different channels in real time. When the signal is saturated, the data processing module sends a command to the laser to reduce the laser power.

[0017] The electrical signal amplitude value is used to monitor whether the ranging function of the equipment is normal. By monitoring the correspondence between the laser output power and the electrical signal amplitude value of the echo light signal, the reception time is compared with the absolute time of the non-saturated signal in different channels selected from the real-time signal to calibrate the delay of the electrical signal in different channels.

[0018] In the preferred scheme, the receiving time is determined by monitoring the correspondence between the laser output power and the electrical signal amplitude of the echo light signal, and by comparing the receiving time corresponding to the non-saturated signal in different channels from the real-time signal with the absolute time.

[0019] If we approximate the echo signal as a Gaussian waveform, with an amplitude of A and an echo signal pulse width constant of τ, then the waveform formula can be approximately written as:

[0020]

[0021] Since the amplitude of the echo signal cannot be determined, the original echo signal needs to be attenuated and delayed. The original signal f(t) is attenuated to obtain f1(t), and delayed by the channel delay signal to obtain f2(t). The two signals are then compared to obtain the output signal f0(t).

[0022] First, the original signal is attenuated. Assuming the attenuation coefficient for the original echo signal amplitude is k, the attenuated signal is as follows:

[0023]

[0024] The signal is delayed by the channel delay signal to obtain f2(t). The time difference obtained by the delay is Δt = t2 - t1, where t2 is the actual measured time and t1 is the reference time obtained in the step. The signal obtained after processing is as follows:

[0025]

[0026] f2(t) is used to obtain the final electrical signal by compensating for the time difference of the delay.

[0027] This invention provides a self-calibration method for the delay of electrical signal channels in a 3D laser scanner. A fixed reflectivity target is installed inside the device outside the working field of view of the 3D laser scanner, enabling self-calibration of inter-channel delays after power-on. This function eliminates the influence of external environmental factors on device delays and facilitates monitoring of device functionality through power-on self-testing. Due to its simple principle, small error, and high accuracy, this project selected the constant ratio discrimination method as the method for determining the echo timing point. Attached Figure Description

[0028] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0029] Figure 1 This is a schematic diagram of the delay self-calibration method of the present invention;

[0030] Figure 2 This is a simplified flowchart illustrating the principle of the self-calibration delay method of the present invention.

[0031] Figure 3 This is a schematic diagram of the steps of the self-calibration method for time delay of the present invention; Detailed Implementation

[0032] Example 1

[0033] like Figures 1-3 As shown, a self-calibration method for delay of electrical signal channel of a three-dimensional laser scanner is provided. S1, a fixed reflective target is installed at an angle position that the laser reflected by the internal scanning mirror of the three-dimensional laser scanner can sweep outside the working field of view of the scanner, and the light rays at the target surface and the target center position are perpendicular.

[0034] S2. The optical path distance d1 between the target surface and the APD photosensitive surface is fixed, the distance d2 between the origin of the scanner coordinate system and the target surface is fixed, and the optical path distance d3 corresponding to the time difference between the emitted pulse and the received pulse should also be fixed.

[0035] Based on this feature, d1, d2, and d3 can be measured and acquired in real time as needed, either at the start of the scanner's operation or during the operation.

[0036] S3. Real-time calibration of the delay parameters of each channel ensures the consistency of the distance measurement benchmark for each channel, as well as the consistency of distance measurement between channels.

[0037] S4. Calculate the time difference between the transmitted pulse and the received pulse using the absolute distance between the target and the transmitting and receiving channels. Add this time difference to the fixed delay between the reference pulse and the transmitted pulse to obtain the absolute time as a reference.

[0038] S5. When the equipment is powered on, the data processing module sends a command to the scanning mechanism to stop the scanning mechanism from illuminating the target with the emitted laser.

[0039] A fixed reflectivity target is installed inside the device outside the working field of view of the 3D laser scanner, enabling self-calibration of inter-channel delays after power-on. This function eliminates the influence of external environmental factors on device delays and facilitates self-testing upon power-on to monitor the device's functionality. Due to its simple principle, small error, and high accuracy, this project selected the constant ratio discrimination method as the method for determining the echo timing point.

[0040] The data processing module sends a command to the transmitting module to control the transmitting module to emit a pulsed laser. At the same time, the pulsed laser emits a reference beam to the analog amplification module as a reference signal.

[0041] The pulsed laser is irradiated onto the target surface by the scanning mechanism. The light signal reflected back by the diffuse reflection enters the receiving channel through the scanning mechanism and converges on the photosensitive element on the surface of the analog detection amplification module. The light signal is then output as electrical signals from different channels to the data processing module by the analog detection amplification module.

[0042] The data processing module compares the electrical signals of different channels with absolute time to calibrate the delay of the electrical signals of different channels.

[0043] like Figure 2As shown, after the device is powered on, the data processing module sends a command to the scanning mechanism, causing the scanning mechanism to stop when the emitted laser shines on the target.

[0044] The data processing module sends a command to the transmitting module to control the transmitting module to emit pulsed laser. At the same time, the pulsed laser emits a reference beam to the analog amplification module as a reference signal. The data processing module controls the power of the emitted pulsed laser in real time, adjusting it from high to low.

[0045] The pulsed laser is irradiated onto the target surface by the scanning mechanism. The reflected light signal is then received by the scanning mechanism and converged on the photosensitive element on the surface of the analog detection amplification module. The light signal is then processed by the analog detection amplification module through photoelectric conversion and output as electrical signals from different channels to the data processing module.

[0046] The data processing module performs waveform analysis on the amplitude values ​​and reception time of electrical signals from different channels in real time. When the signal is saturated, the data processing module sends a command to the laser to reduce the laser power.

[0047] Example 2

[0048] Further explanation in conjunction with Example 1, such as Figure 1-3 The structure shown uses the electrical signal amplitude value to monitor whether the ranging function of the device is normal. By monitoring the correspondence between the laser output power and the electrical signal amplitude value of the echo light signal, the reception time is compared with the absolute time of the non-saturated signal in different channels selected from the real-time signal to calibrate the delay of the electrical signal in different channels.

[0049] In the preferred scheme, the receiving time is determined by monitoring the correspondence between the laser output power and the electrical signal amplitude of the echo light signal, and by comparing the receiving time corresponding to the non-saturated signal in different channels from the real-time signal with the absolute time.

[0050] Lasers emit modulated, regular, narrow pulse signals. The echo signal, after diffuse reflection from the object being measured, becomes irregular and is affected by various factors such as distance, atmospheric conditions, and target reflectivity. The waveform of the echo signal is completely different from the emitted pulsed laser signal. For laser ranging, the accuracy of time measurement determines the accuracy of distance measurement; therefore, the timing of the echo signal is crucial. This scheme employs a constant ratio discrimination method. As the name suggests, the constant ratio method uses a fixed ratio position (usually the midpoint of the leading edge) of the echo pulse amplitude as the timing point of the echo signal. The timing point of the constant ratio method is independent of the echo signal amplitude and only depends on the set ratio point.

[0051] If we approximate the echo signal as a Gaussian waveform, with an amplitude of A and an echo signal pulse width constant of τ, then the waveform formula can be approximately written as:

[0052]

[0053] Since the amplitude of the echo signal cannot be determined, the original echo signal needs to be attenuated and delayed. The original signal f(t) is attenuated to obtain f1(t), and delayed by the channel delay signal to obtain f2(t). The two signals are then compared to obtain the output signal f0(t).

[0054] First, the original signal is attenuated. Assuming the attenuation coefficient for the original echo signal amplitude is k, the attenuated signal is as follows:

[0055]

[0056] The signal is delayed by the channel delay signal to obtain f2(t). The time difference obtained by the delay is Δt = t2 - t1, where t2 is the actual measured time and t1 is the reference time obtained in the step. The signal obtained after processing is as follows:

[0057]

[0058] f2(t) is used to obtain the final electrical signal by compensating for the time difference of the delay. The constant ratio discrimination method is simple in principle, has small error and high accuracy, so this project chose the constant ratio discrimination method as the method for determining the timing point of the echo.

[0059] The above embodiments are merely preferred technical solutions of the present invention and should not be considered as limitations on the present invention. The scope of protection of the present invention should be limited to the technical solutions described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A method for self-calibrating the delay of the electrical signal channel of a three-dimensional laser scanner, characterized in that: S1. Install a fixed reflective target at an angle that the laser can sweep through the internal scanning mirror of the 3D laser scanner outside the working field of view of the 3D laser scanner, with the target surface perpendicular to the light at the target center. S2, Optical path distance between the target surface and the APD photosensitive surface It is a fixed distance between the origin of the scanner coordinate system and the target surface. It is constant; the optical path distance corresponding to the time difference between the transmitted and received pulses is fixed. It should also be fixed and unchanging; Real-time measurement and acquisition at the start or during the scanner's operation , , ; S3. Real-time calibration of the delay parameters of each channel ensures the consistency of the distance measurement benchmark for each channel, as well as the consistency of distance measurement between channels. S4. Calculate the time difference between the transmitted pulse and the received pulse using the absolute distance between the target and the transmitting and receiving channels. Add this time difference to the fixed delay between the reference pulse and the transmitted pulse to obtain the absolute time as a reference. S5. When the equipment is powered on, the data processing module sends a command to the scanning mechanism to stop the scanning mechanism from illuminating the target with the emitted laser. The data processing module sends a command to the transmitting module to control the transmitting module to emit a pulsed laser. At the same time, the pulsed laser emits a reference beam to the analog amplification module as a reference signal. The pulsed laser is irradiated onto the target surface by the scanning mechanism. The light signal reflected back by the diffuse reflection enters the receiving channel through the scanning mechanism and converges on the photosensitive element on the surface of the analog detection amplification module. The light signal is then output as electrical signals from different channels to the data processing module by the analog detection amplification module. The data processing module compares the electrical signals from different channels with absolute time to calibrate the delay of the electrical signals from different channels. After the equipment is powered on, the data processing module sends a command to the scanning mechanism to stop the scanning mechanism from illuminating the target with the emitted laser. The data processing module sends a command to the transmitting module to control the transmitting module to emit pulsed laser. At the same time, the pulsed laser emits a reference beam to the analog amplification module as a reference signal. The data processing module controls the power of the emitted pulsed laser in real time, adjusting it from high to low. The pulsed laser is irradiated onto the target surface by the scanning mechanism. The reflected light signal is then received by the scanning mechanism and converged on the photosensitive element on the surface of the analog detection amplification module. The light signal is then processed by the analog detection amplification module through photoelectric conversion and output as electrical signals from different channels to the data processing module. The data processing module performs waveform analysis on the amplitude values ​​and reception time of electrical signals from different channels in real time. When the signal is saturated, the data processing module sends a command to the laser to reduce the laser power. The electrical signal amplitude value is used to monitor whether the ranging function of the equipment is normal. By monitoring the correspondence between the laser output power and the electrical signal amplitude value of the echo light signal, the reception time is compared with the absolute time of the non-saturated signal in different channels selected from the real-time signal to calibrate the delay of the electrical signal in different channels. By monitoring the correspondence between the laser output power and the electrical signal amplitude of the echo light signal, the reception time is compared with the absolute time by selecting the reception time corresponding to the non-saturated signal in different channels from the real-time signal. The echo signal is approximated as a Gaussian waveform, with an amplitude of... The echo signal pulse width constant is Then the formula for the waveform can be approximately written as: ； Since the amplitude of the echo signal cannot be determined, it is necessary to attenuate and delay the original echo signal to reduce its amplitude. Signal attenuation was performed separately to obtain Obtained by delaying the channel delay signal The output signal is obtained after the two signals pass through the comparator. ; First, the original signal is attenuated. Assume the attenuation coefficient for the original echo signal amplitude is... k The signal after attenuation is as follows: ； Obtained by delaying the channel delay signal. The time difference obtained by the delay is , For the actual measured time, Given the reference time obtained in the steps, the processed signal is as follows: ； The final electrical signal is obtained by compensating for the time difference caused by the delay.

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