Laser pulse ranging echo differential processing algorithm

Abstract

The invention discloses a differential processing algorithm for laser pulse ranging echoes, which is characterized in that the echoes of laser pulse signals are differentiated through a mathematical method, so that an extreme point, namely the peak moment of the echoes, is solved. According to the differential processing algorithm of the laser pulse ranging echo, the extreme point is obtained by differentiating the Gaussian signal of the time t. The change of the intensity of the echo does not cause the change of the extreme point moment, i.e., the t0 moment is not changed, so that the method fundamentally eliminates the moment discrimination error delta t of the leading edge discrimination method, naturally does not need to be optimized to obtain the dual-threshold leading edge discrimination method, and also avoids the problems of other methods in use. When the echo size changes, the peak moment can still be accurately identified, the drift error is greatly eliminated, in the pulse laser ranging echo moment identification method, the accuracy is far higher than that of other methods, linear fitting and other secondary error compensation are not needed, the engineering complexity is reduced, the workload is reduced, and the adaptability is improved.

Description

Technical Field

[0001] The present invention relates to a differential processing algorithm for laser pulse ranging echoes, belonging to the technical field of pulsed laser ranging. Background Art

[0002] At present, the time discrimination of pulsed laser ranging echoes includes the following methods:

[0003] 1. Leading-edge discrimination method:

[0004] The principle of the leading-edge discrimination method is to set a threshold. When the level of the echo signal is greater than the set threshold, the moment at this time is used as the start and end moments of the time interval. Its basic principle is as Figure 1 shown.

[0005] The circuit design of leading-edge time discrimination is relatively simple compared with other discrimination methods. The main component of the circuit is a high-speed comparator. This comparator compares the level of the echo signal with a preset threshold, and takes the moment when the pulse level is greater than the threshold as the start and end moments. However, the influence caused by noise needs to be considered. The setting of the threshold must be greater than the moment false trigger caused by the noise level. Although the leading-edge discrimination method has a simple design, there are errors. First, it sets a fixed threshold, and due to the influence of external factors such as the atmosphere on the echo signal, large distortions will occur, and the moment when the corresponding pulse level is higher than the threshold point will change. Second, geometric drift errors will occur during the design process, whether it is an ideal receiver or a non-ideal receiver. Finally, the time delay generated by the comparator during operation is also a cause of error.

[0006] 2. Double-threshold leading-edge discrimination method

[0007] The double-threshold leading-edge time discrimination method belongs to an improvement of the leading-edge discrimination method, and its working principle is as Figure 2 shown.

[0008] The reference signal generates a start timing digital signal through threshold V th . The echo signal simultaneously generates two stop timing digital signals through V th1 and V th2 (V th1 <V th2 ). The dotted line and the solid line are used to represent echo signals with different intensities respectively. Two flight times t1 and t2 (t ′ 1 and t ′ 2) can be measured for the same echo signal. This method converts the time discrimination error Δt caused by the size of the echo signal into (V th2 -V th1 / t2 - t1)-(V th2 -V th1 / t′ 2 - t ′ 1) That is, the change in slope. This change value can be recorded and then processed by other methods such as first - order linear fitting to reduce the error.

[0009] 3. Other methods:

[0010] To eliminate the time - drift error, other common methods for discriminating the laser echo time mainly include the constant - ratio discrimination method, the high - pass capacitive - resistive discrimination method, and the error - compensation discrimination method. The constant - ratio discrimination method uses the moment when the half - height point of the leading edge of the laser echo signal arrives as the stop moment of the laser echo. The high - pass capacitive - resistive discrimination method utilizes the differential effect of the high - pass capacitive - resistive filter circuit to transform the peak point of the laser echo signal into a zero point, and uses this as the stop moment of the laser echo. The error - compensation method measures the same laser echo signal with multiple thresholds and uses the calibrated error - compensation relationship to compensate for the time - drift error caused by a single threshold to obtain the accurate stop moment of the laser echo.

[0011] The leading - edge duration of the laser echo signal is very short (such as in the picosecond range), which increases the circuit design and processing difficulty of the constant - ratio discrimination method and the high - pass capacitive - resistive discrimination method. Worse still, both the constant - ratio discrimination method and the high - pass capacitive - resistive discrimination method require that the echo signal does not saturate, making it difficult to adapt to the occasion where the echo intensity changes violently. And the error - compensation discrimination requires continuous debugging and linear fitting, with a low technical content, greatly increasing the engineering complexity and workload. Summary of the Invention

[0012] The present invention provides a differential processing algorithm for laser - pulse ranging echoes, which can accurately and effectively identify the laser echo time and echo peak. When the echo size changes, it can still accurately identify the peak moment, greatly eliminating the drift error. Among the methods for discriminating the laser - pulse ranging echo time, the accuracy is much higher than other methods, and it does not require secondary error compensation such as linear fitting, reducing the engineering complexity and workload.

[0013] To solve the above - mentioned technical problems, the technical solutions adopted by the present invention are as follows:

[0014] A differential processing algorithm for laser - pulse ranging echoes, which performs differentiation on the echo of the laser - pulse signal through a mathematical method to find the extreme point, that is, the peak moment of the echo.

[0015] This application adopts a brand - new method, no longer using the one - size - fits - all leading - edge discrimination method, nor using the method of locking the stable door after the horse has bolted and requiring debugging and fitting to increase the complexity and workload like the double - threshold leading - edge discrimination method. At the same time, it avoids the problems existing in other methods (such as the constant - ratio discrimination method, the high - pass capacitive - resistive discrimination method, and the error - compensation discrimination method).

[0016] This patent proposes a new method for moment discrimination. By means of mathematics, the echo of the laser pulse signal is differentiated to find the extreme point, that is, the peak moment of the echo.

[0017] The echo signal of a pulsed laser rangefinder is generally a Gaussian signal. Gaussian signals follow a normal distribution, also known as a Gaussian distribution. The Gaussian function is the mathematical expression of a Gaussian signal and is usually denoted by the symbol f(x). In one dimension, the Gaussian function can be expressed as:

[0018]

[0019] Where:

[0020] ● f(x) is the mathematical function representation of the Gaussian signal;

[0021] ● μ is the mean;

[0022] ● σ is the standard deviation, which determines the width of the curve;

[0023] ● x is the independent variable, representing different value points of the signal;

[0024] ● exp(*) represents the exponential function.

[0025] In the application scenario of laser ranging, the echo signal is generally a Gaussian signal with respect to time t, and the expression is:

[0026]

[0027] Where:

[0028] ● s(t) is the amplitude of the Gaussian pulse signal at time t;

[0029] ● A is the peak value of the Gaussian pulse signal;

[0030] ● t0 is the center time of the Gaussian pulse signal;

[0031] ● σ is the standard deviation of the Gaussian pulse signal, which controls the width and shape of the pulse;

[0032] ● t0 and r are parameters related to a specific application scenario. For example, in a Gaussian signal considering time correlation, t0 may be related to the initial moment of the pulse, while r is related to the width or shape of the pulse;

[0033] ● exp(*) represents the exponential function.

[0034] We differentiate the Gaussian signal with respect to time t to obtain the extreme points. Theoretically, the change in the strength of the echo does not cause a change in the time of the extreme points, that is, the time t0 remains unchanged. Therefore, this method fundamentally eliminates the time discrimination error Δt of the leading edge discrimination method. Naturally, there is no need to optimize it to obtain the dual-threshold leading edge discrimination method, and it also avoids the problems in the use of other methods. The only requirement is a relatively high computing power for the single-chip microcomputer, that is, the MCU (central controller), to meet the requirements of rapid measurement in laser ranging. With the development of electronic information technology and the chip industry, there are many high-performance chips with good computing power on the market, and the prices are not expensive.

[0035] The following elaborates on the specific differential algorithm.

[0036] Let the Gaussian signal be: where a, b, and c are constants, and c > 0.

[0037] Now, differentiate with respect to time t, that is, find

[0038] Using the chain rule and the derivative rule of the exponential function, we have:

[0039]

[0040] Therefore, the Gaussian pulse signal The derivative with respect to time t is:

[0041] From the differential expression and the echo Gaussian signal expression, it can be seen that the time t = t0 is the extreme point of the signal, and the corresponding signal amplitude value s(t0) is the peak value A of the Gaussian pulse signal.

[0042] Using the ADC acquisition function of the single-chip microcomputer MCU, the echo signal of the laser pulse ranging is completely captured, and DMA transmission is used. After the transmission is completed, an interrupt is triggered, and the main program calls the differential algorithm to calculate the exact value of t0, denoted as t 先 , wait for the next echo, repeat the above differential algorithm to obtain t0, denoted as t 现 , distance = speed of light * (t 现 - t 先 ).

[0043] Technologies not mentioned in this invention shall refer to the prior art.

[0044] The differential processing algorithm for the echo of the laser pulse ranging of the present invention obtains the extreme point by differentiating the Gaussian signal with respect to time t. The change in the strength of the echo will not cause a change in the time of the extreme point, that is, the time t0 remains unchanged. Therefore, this method fundamentally eliminates the time discrimination error Δt of the leading-edge discrimination method. Naturally, there is no need to optimize it to obtain the dual-threshold leading-edge discrimination method, and it also avoids the problems in the use of other methods. When the size of the echo changes, it can still accurately identify the peak time, greatly eliminating the drift error. In the time discrimination method of the pulsed laser ranging echo, the accuracy is much higher than that of other methods, and there is no need for secondary error compensation such as linear fitting, reducing the engineering complexity, reducing the workload, and improving the adaptability. Description of the Drawings

[0045] Figure 1 It is the basic schematic diagram of the leading-edge discrimination method.

[0046] Figure 2 It is the basic schematic diagram of the dual-threshold leading-edge discrimination method.

[0047] Figure 3 It is the basic original diagram of the differential method. Detailed Implementation Manner

[0048] To better understand the present invention, the content of the present invention will be further clarified below in conjunction with embodiments. However, the content of the present invention is not limited to the following embodiments.

[0049] Embodiment 1

[0050] A differential processing algorithm for the echo of the laser pulse ranging obtains the extreme point, that is, the peak time of the echo, by differentiating the echo of the laser pulse signal through a mathematical method.

[0051] The laser pulse signal is where a, b, and c are constants, and c > 0;

[0052] Differentiating with respect to time t, that is, finding

[0053] Using the chain rule and the derivative rule of the exponential function, we have:

[0054]

[0055] That is, the Gaussian pulse signal The differential with respect to time t is: The time t = t0 is the extreme point of the signal, and the corresponding signal amplitude value s(t0) is the peak A of the Gaussian pulse signal.

[0056] Using the ADC acquisition function of the microcontroller MCU, the echo signal of pulsed laser ranging is completely captured, and DMA transmission is used. After the transmission is completed, an interrupt is triggered, and the main program calls the differential algorithm to calculate the exact value of the t0 moment, denoted as t 先 , wait for the next echo, and repeat the above process to obtain t0, denoted as t 现 , distance = speed of light * (t 现 -t 先 ).

[0057] Applying the above algorithm to a high-repetition-rate pulsed laser rangefinder can meet various ranging scenarios such as high and low speeds and static targets of the object. It can be applied to road building measurement, engineering surveying and mapping, intelligent transportation, industrial automation production control, land transportation, security monitoring, lidar, etc. Especially, it can achieve rapid detection and positioning on dynamic targets such as laser fuzes, missile-borne mechanisms, and anti-drone devices. In this example, the STM32F103RCT6 microcontroller is used as the hardware platform for software burning, and the core idea of this algorithm (differential method) is implemented in C language. The Nyquist sampling theorem is used to collect the laser signal demodulated by the APD (avalanche diode). With the precise discrimination of time by the laser pulse ranging echo differential processing algorithm and the filtering of Gaussian noise by the Kalman filter, for a handheld device using conventional pulse ranging, a ranging effect with a ranging range of 1 kilometer and a ranging accuracy of 0.5 m can be achieved.

Claims

1. A differential processing algorithm for laser pulse ranging echoes, characterized in that: Differentiate the echo of the laser pulse signal mathematically to find the extreme point, that is, the peak time of the echo.

2. The differential processing algorithm for the laser pulse ranging echo according to claim 1, wherein: The laser pulse signal is where a, b, and c are constants, and c > 0; Differentiate with respect to time t, that is, find Using the chain rule and the derivative rule of the exponential function, we have: That is, the laser pulse signal The derivative with respect to time t is: The time t = t0 is the extreme point of the signal, and the corresponding signal amplitude value s(t0) is the peak value A of the Gaussian pulse signal.

3. The differential processing algorithm for the laser pulse ranging echo according to claim 2, wherein: Utilize the ADC acquisition function of the microcontroller MCU to fully capture the echo signal of laser pulse ranging, use DMA transmission, trigger an interrupt after the transmission is complete, and the main program calls the differential algorithm to calculate the exact value of the t0 moment, denoted as t 先 , wait for the next echo, repeat the differential algorithm to obtain t0, denoted as t 现 , distance = speed of light * (t 现 -t 先 ).

Images